add_shortcode in functions.php output in wrong order

Hi,

I’m using add_shortcode in the functions.php and when I use it in a page it does output in the wrong order.

Background.
I’m using the below function in functions.php where I read a seperate php file which only contains some html. I do this, because the content of this snippet of html does change periodically and is used in different places also outside of WP and I want to change it only in one place.

function laden_offen_snippet() {
	$laden_offen = file_get_contents('offen.php', false);
	echo $laden_offen;
}
add_shortcode('offen', 'laden_offen_snippet');

In the WP page where I use it there is something like this:

<h1>Title</h1>
[offen]
<p>some paragraph</p>

but the problem is that the part of [offen] appears before the Title in the output.
May do I wrong when I use echo in the function above?
Or any other idea, how to get on the right place?
Thanks a lot
Tom