headers already stated and 1 character of unexpected output

I am making a simple plugin that will filter search via categories and it works but after I activate the plugin I get “1 characters of unexpected output sent” and also “headers already sent” error on post updates etc.

What do I need to change in my code so that doesn’t appear?

$search_text = '';
$default_cat = 'all'; // default option in category dropdown
$excluded_cats = array(); // raw
$clean_excluded_cats = array();
$cat_text = '';

add_option('vkssfl_search_text', $search_text);
add_option('vkssfl_default_cat', $default_cat);
add_option('vkssfl_excluded_cats', $excluded_cats);
add_option('vkssfl_clean_excluded_cats', $clean_excluded_cats);
add_option('vkssfl_cat_text', $cat_text);
add_option('vkssfl_cat_style', $cat_style);

// add options page

function vkssfl_add_config_page() {
    add_options_page(
        'Super Search Filter Lite Options',
        'Super Search Filter Lite',
        'manage_options',
        basename(__FILE__),
        'vkssfl_config_page'
    );
}
add_action('admin_menu', 'vkssfl_add_config_page');

// make the config options
function vkssfl_config_page() {

    // if options are submitted (from admin)
    if (isset($_POST['submit'])) {

        // some security checks
        $nonce = $_REQUEST['_wpnonce'];
        if (! wp_verify_nonce($nonce, 'vkssflfp-updatesettings' ) ) {
            die('security error');
        }
        if (! current_user_can('manage_options') ) {
                die('you can\'t manage options');
        }
        check_admin_referer('vkssflfp-updatesettings');

        // get new option values
        $search_text = $_POST['search-text'];
        $meta_search_key = $_POST['meta_search_key'];
        $default_cat = $_POST['default-cat'];
        $excluded_cats = $_POST['post_category'];

        // fix return values
        $fix = (array)$_POST['post_category'];
        array_unshift($fix, '1');
        $clean_excluded_cats = implode(',' , $fix);

        $cat_text = $_POST['cat-text'];

        if ($_POST['cat_style'] == 'checkbox') {
            $cat_style = 'checkbox';
        } elseif ($_POST['cat_style'] == 'dropdown') {
            $cat_style = 'dropdown';
        } else if ($_POST['cat_style'] == 'none') {
            $cat_style = 'none';
        } else {
            $cat_style = 'none';
        }

        // update options in the db
        update_option('vkssfl_search_text', $search_text);
        update_option('vkssfl_default_cat', $default_cat);
        update_option('vkssfl_excluded_cats', $excluded_cats);
        update_option('vkssfl_clean_excluded_cats', $clean_excluded_cats);
        update_option('vkssfl_cat_text', $cat_text);
        update_option('vkssfl_cat_style', $cat_style);  

    } // end if options are submitted (from admin)

    // get options from the db
    $search_text = get_option('vkssfl_search_text');
    $default_cat = get_option('vkssfl_default_cat');
    $excluded_cats = get_option('vkssfl_excluded_cats');
    $clean_excluded_cats = get_option('vkssfl_clean_excluded_cats');
    $cat_text = get_option('vkssfl_cat_text');
    $cat_style = get_option('vkssfl_cat_style');

    ?>

    <div class="wrap">
        <h2>Super Search Filter LITE options</h2>

        <form action="" method="post" id="sbc-config">

            <table class="form-table">
<?php wp_nonce_field('vkssflfp-updatesettings'); ?>
            <tr>
                <th scope="row" valign="top">
                <label for="search-text">
                    Display text inside the search box:
                </label>
                </th>
                <td>
                    <input type="text" name="search-text" id="search-text" class="regular-text" value="<?php echo $search_text; ?>">
                </td>
            </tr>

            <tr>
                <th scope="row" valign="top">
                <label for="search-text">
                    Display categories as:
                </label>
                </th>
                <td>
<?php $gcs = get_option('vkssfl_cat_style'); ?>
                    <input type="radio" name="cat_style" id="cb" value="checkbox" <?php if ($gcs == 'checkbox') echo 'checked="checked"'; ?>>
                    <label for="cb">Checkbox</label>
                    <input type="radio" name="cat_style" id="dd" value="dropdown" <?php if ($gcs == 'dropdown') echo 'checked="checked"'; ?>>
                    <label for="dd">Dropdown</label>
                    <input type="radio" name="cat_style" id="none" value="none" <?php if ($gcs != 'dropdown' && $gcs != 'checkbox') echo 'checked="checked"'; ?>>
                    <label for="none">None</label>
                </td>
            </tr>

            <tr>
                <th scope="row" valign="top">
                <label for="search-text">
                    Search categories text:
                </label>
                </th>
                <td>
                    <input type="text" name="cat-text" id="search-text" class="regular-text" value="<?php echo $cat_text; ?>">
                </td>
            </tr>

            <tr>
                <th scope="row" valign="top">
                <label for="default-cat">
                    Display text to choose all categories:
                </label>
                </th>
                <td>
                    <input type="text" name="default-cat" id="default-cat" class="regular-text" value="<?php echo $default_cat; ?>">
                </td>
            </tr>

            <tr>
                <th>
                <label for="focus">Categories to exclude:</label>
                </th>
                <td><ul><?php wp_category_checklist(0,0,$excluded_cats); ?></ul></td>
            </tr>

            </table>

            <p class="submit"><input type="submit" value="Save Changes" class="button button-primary" id="submit" name="submit"></p>

            </form>
        </div>
<?php
} // end vkssfl_config_page()

function vkssfl_form() {

    // get options from the db
    $search_text = get_option('vkssfl_search_text');
    $default_cat = get_option('vkssfl_default_cat');
    $excluded_cats = get_option('vkssfl_excluded_cats');
    $clean_excluded_cats = get_option('vkssfl_clean_excluded_cats');

    $settings = array(
    'show_option_all'    => $default_cat,
    'show_option_none'   => '',
    'orderby'            => 'id',
    'order'              => 'ASC',
    'show_count'         => 0,
    'hide_empty'         => 0,
    'child_of'           => 0,
    'exclude'            => "'".$clean_excluded_cats."'",
    'echo'               => 0,
    'selected'           => 0,
    'hierarchical'       => 0,
    'name'               => 'cat',
    'id'                 => '',
    'class'              => 'postform',
    'depth'              => 0,
    'tab_index'          => 0,
    'taxonomy'           => 'category',
    'hide_if_empty'      => false,
    'walker'             => ''
    ); 

    $list = wp_dropdown_categories($settings);

    $blog_url = get_bloginfo('url');

    ?>
    <div id="vkssfl">
    <form method="get" action="<?php echo $blog_url; ?>" id="vkssfl-search" name="vkssflfp-config">
        <input type="text" value="<?php echo $search_text; ?>" name="s" id="s" />
<?php $cat_title = get_option('vkssfl_cat_text'); ?>
<?php echo '<div>'; ?>
<?php if (!empty($cat_title)) echo "<h4>$cat_title</h4>"; ?>
<?php
        // make checkboxes from categories
        $args = array(
                'exclude' => $excluded_cats,
                'orderby' => 'id',
                'order' => 'ASC'
            );
        $t = get_categories($args);
        // print_r($t);
        $cat_style = get_option('vkssfl_cat_style');;
        if ($cat_style == 'checkbox') {
            foreach ($t as $v) {
            echo "<p><input type=\"checkbox\" name=\"get_cb[]\" value=\"$v->cat_ID\" id=\"$v->name\" /><label for=\"$v->name\"> $v->name</label></p>";
            }
        } elseif ($cat_style == 'dropdown') {
        echo $list;
        }
        echo '</div>';
        ?>
        <p class="ssbtn"><button>Submit</button></p>
    </form>
    </div>
<?php

} // end vkssfl_form()

function vkssfl_super_search($query) {

    // has the form been init?
    if (isset($_GET['s'])) {

        // get excluded cats
        $excluded_cats = get_option('vkssfl_excluded_cats');

        //make the query
        $s = filter_input(INPUT_GET, 's', FILTER_SANITIZE_STRING);
        // if ( empty( $s ) ) return;
        $query->is_search = true;
        $query->set( 's', $s );
        $query->set( 'category__not_in', $excluded_cats );

        // get which category chekboxes were checked
        if (isset($_GET['get_cb'])) {
            $get_cb = $_GET['get_cb'];
            foreach ($get_cb as $value) {
                $cbid .= ','.$value;
            }
            $cbid = ltrim($cbid, ',');
            $new_cbid = explode(',', $cbid);
        }
        if (isset($_GET['get_cb'])) {
            $query->set( 'category__in', $new_cbid );
        }

    } // end has the form been init?

} // end vkssfl_super_search()
add_action('pre_get_posts', 'vkssfl_super_search');

// add display hooks
add_shortcode('vkssfl', 'vkssfl_form');
add_filter('widget_text', 'do_shortcode');