Custom template for Essential grid posts WordPress plugin

I use Essential Grid Posts plugin, I would like to create a custom template for posts I create in Ess. Grid Posts

Usually to create custom template for post that belong to a category I use the following code:

<?php

$post = $wp_query->post;

if ( in_category('3') ) {

include(TEMPLATEPATH . '/single-1.php');

} elseif ( in_category('7') ) {

include(TEMPLATEPATH . '/single-2.php');

} else {

include(TEMPLATEPATH . '/single-default.php');

}

?>

But it doesn’t work with the id category of Essential grid post. What’s wrong?