What am I doing wrong?

I am writing some code to allow me to have a find and replace function using a shortcode, this bit worked fine, until I tried to add arguments to the shortcode.
The second I started trying to have arguments/attributes for the URL query and replacement word, it all went to pot.

The code can be found below, I am new to PHP and have no idea what I have done wrong, this is VERY different to the other languages I have worked with (mostly c#).

add_filter('query_vars', 'parameter_queryvars' );
function parameter_queryvars( $qvars )
{
$qvars[] = 'productname';
return $qvars;
}

//Register Shortcode

function legal_content_function($atts, $content = null) {

	?>
	<div class="et_pb_row"">
	<?php

$atts = shortcode_atts(
		array(
			'query' => 'productname',
			'replace' => '=productname=',
			), $atts);
	global $wp_query;
if (isset($wp_query->query_vars[$atts['query']]))
{
echo str_replace($atts['replace'], $wp_query->query_vars[$atts['query']], $content);
}
else
{
echo "<h1>Error</h1>";
echo "Please use URl query \"?productname=\" to display this page.";
}
}

function register_shortcodes(){
	add_shortcode('legalcontent', 'legal_content_function');
}
add_action( 'init', 'register_shortcodes');

function dlp_settings_menu(){
        add_options_page( 'Dynamic Legal Page', 'Dynamic Legal Page Settings', 'manage_options', 'dlp-plugin', 'dlp_init' );
}
add_action('admin_menu', 'dlp_settings_menu');

function dlp_init(){
	echo "<h2>Settings</h2>";
	echo "<h2>Usage</h2>";
	echo "<h2>Credits</h2>";
}
?>