[help] Trying to make a “hello world” like plugin

Hi guys!

As the title indicates, I’m trying to work my way arround into making a “hello dolly” like plugin, but, instead of echoing text to the admin footer, I want it to echo to the loop_end. I’m also trying to make this as simple as it comes (1 file), so i can understand it, and, eventually, do something better next time.

Here’s the entire code:

<?php
// Hook for adding admin menus
add_action('admin_menu', 'mt_add_pages');

// action function for above hook
function mt_add_pages() {
    // Add a new top-level menu (ill-advised):
    add_menu_page('Hello World', 'Hello World', 'administrator', 'mt-top-level-handle', 'mt_toplevel_page');
}

// mt_sublevel_page() displays the page content for the first submenu
// of the custom Test Toplevel menu
function mt_toplevel_page() {

    // variables for the field and option names
    $opt_name = 'mt_favorite_food';
    $hidden_field_name = 'mt_submit_hidden';
    $data_field_name = 'mt_favorite_food';

    // Read in existing option value from database
    $opt_val = get_option( $opt_name );

    // See if the user has posted us some information
    // If they did, this hidden field will be set to 'Y'
    if( $_POST[ $hidden_field_name ] == 'Y' ) {
        // Read their posted value
        $opt_val = $_POST[ $data_field_name ];
        // Save the posted value in the database
        update_option( $opt_name, $opt_val );

        // Put an options updated message on the screen

?>

<div class="updated">
  <p><strong>
    <?php _e('Options saved.', 'mt_trans_domain' ); ?>
    </strong></p>
</div>
<?php

    }

    // Now display the options editing screen

    echo '<div class="wrap">';

    // header

    echo "<h2>" . __( 'Menu Test Plugin Options', 'mt_trans_domain' ) . "</h2>";

    // options form

    ?>
<form name="form1" method="post" action="">
  <input type="hidden" name="<?php echo $hidden_field_name; ?>" value="Y">
  <p>
    <?php _e("Favorite Color:", 'mt_trans_domain' ); ?>
    <input type="text" name="<?php echo $data_field_name; ?>" value="<?php echo $opt_val; ?>" size="20">
  </p>
  <hr />
  <p class="submit">
    <input type="submit" name="Submit" value="<?php _e('Update Options', 'mt_trans_domain' ) ?>" />
  </p>
</form>
</div>
<?php
show_my_data($opt_val);

};
function show_my_data($val) {
	$myvar =  "<h2>".$val."</h2>";
	echo $myvar;

}
add_action('loop_end', 'show_my_data');
?>

The problem is that it’s echoing the data to the plugin admin page, and throwing me a “Catchable fatal error” on the end of the loop.

Any ideas? Any tips would come in handy!
Thanks a bunch!
Regards