Preset text in editor

Hello folks, i tried this piece of code to preset some text in the editor in the functions.php:

<?php

add_filter( 'default_content', 'my_editor_content' );

function my_editor_content( $content ) {

	$content = "This is some custom content I'm adding to the post editor because I hate re-typing it.";

	return $content;
}

?>

But, when i add html code like this:

.....
function my_editor_content( $content ) {

	$content = "<img src="" width="100%" height="100%">
text
<h3>Download</h3>
<a href="" target="_blank"></a>";

.....

?>

it doesnt work. I understand why, because all the “” are fighting with eachother, but how should i write that piece of code so that it works in the editor? Now tha whole page gets white, and i have to reupload the backup php file to make my site work again.