Add content after $content

I am trying to do something pretty simple but I can’t seem to get it to work I think I have followed the codex but I must have done something wrong I can’t see.

In the wordpress admin I have added a few lines of text to one page (id=5) and I want to add a simple form that I have coded in a seperate php file after this text. This is the code I have in my custom functions file in my child theme. It all works – BUT – the form appears above the page text and I want it to appear after.

function notifications_page($content) {
 if (is_page('5')) {
	include get_stylesheet_directory() . '/notifications_functions.php';
}
  return $content;
}
add_filter('the_content', 'notifications_page');