Header display on a php page

Hello,

we’re using GP Pro.

I have a php file that is called from a GP Wordpress page.

I have included header and footer in the php file with the functions get_header() and get_footer(). The footer is displayed correctly.
There are the following problems with the header:
- at high resolutions (more than 1400px width; container has 1400px) the primary navigation is not displayed over the full screen width
- the logo is displayed twice

When scrolling down, the pinned primary navigation is displayed correctly.

Here is an example page:
https://www.trueffelsuche.com/wp-content/plugins/aaa_plugin_button/watchlist_eintrag_test.php

Here is the code of the php page:

<?php

$path = $_SERVER['DOCUMENT_ROOT'];

include_once $path . '/wp-load.php';
include_once $path . '/wp-includes/wp-db.php';

if ( ! defined( 'ABSPATH' ) ) {
	exit; // Exit if accessed directly.
}

get_header();

	echo "<br><br><br><br><br><br><br>";
	echo "Test 1234 <br>";		
	echo "Watchlisten-Eintrag: ";
	echo "Test 5678 <br>";
	echo "<br><br><br><br><br><br><br>";
	echo "Test 1234 <br>";		
	echo "Watchlisten-Eintrag: ";
	echo "Test 5678 <br>";
	echo "<br><br><br><br><br><br><br>";
	echo "Test 1234 <br>";		
	echo "Watchlisten-Eintrag: ";
	echo "Test 5678 <br>";
	echo "<br><br><br><br><br><br><br>";
	echo "Test 1234 <br>";		
	echo "Watchlisten-Eintrag: ";
	echo "Test 5678 <br>";
	echo "<br><br><br><br><br><br><br>";
	echo "Test 1234 <br>";		
	echo "Watchlisten-Eintrag: ";
	echo "Test 5678 <br>";
	echo "<br><br><br><br><br><br><br>";
	
get_footer();

Can you help me, please?

Thank you.