Custom Post type dont use custom page template (slug is not right)

I created a custom post type ‘gruppen’ and a custom page templete ‘page-gruppen.php’. I want to use ‘page-gruppen.php’ to show my custom post type content but the custom post type uses always the normal wp template ‘page.php’

When i print the slug it gives the last post name and not gruppen.

What is my failure?

this is my post typ:

function gruppen_post_type() {
    $labels = array(
        'name'                  => _x( 'Gruppen', 'Post Type General Name' ),
        'singular_name'         => _x( 'Gruppe', 'Post Type Singular Name' ),
        'menu_name'             => 'Gruppen',
        'name_admin_bar'        => 'Gruppen',
        'archives'              => 'Gruppe Archives',
        'attributes'            => 'Gruppe Attributes',
        'parent_item_colon'     => 'Gruppe parent:',
        'all_items'             => 'All Gruppen',
        'add_new_item'          => 'Neue Gruppe hinzufügen',
        'add_new'               => 'Gruppe hinzufügen',
        'new_item'              => 'Neue Gruppe',
        'edit_item'             => 'Gruppe editieren',
        'update_item'           => 'Gruppe aktualisieren',
        'view_item'             => 'Gruppe anzeigen',
        'view_items'            => 'Gruppen anzeigen',
        'search_items'          => 'Gruppe suchen',
        'not_found'             => 'Not found',
        'not_found_in_trash'    => 'Not found in Trash',
        'featured_image'        => 'Featured Image',
        'set_featured_image'    => 'Set featured image',
        'remove_featured_image' => 'Remove featured image',
        'use_featured_image'    => 'Use as featured image',
        'insert_into_item'      => 'In Gruppe einfügen',
        'uploaded_to_this_item' => 'Uploaded to this Gruppe',
        'items_list'            => 'Gruppe list',
        'items_list_navigation' => 'Gruppen list navigation',
        'filter_items_list'     => 'Filter Gruppen list'
    );
    $args = array(
        'rewrite'               => array( 'slug' => 'gruppen' ),
        'label'                 => 'Gruppe Post Type',
        'description'           => 'Gruppe erfassen',
        'labels'                => $labels,
        'supports'              => array( 'title', 'editor', 'excerpt' ),
        'hierarchical'          => true,
        'public'                => true,
        'show_ui'               => true,
        'show_in_menu'          => true,
        'menu_position'         => 6,
        'menu_icon'             => 'dashicons-groups',
        'show_in_admin_bar'     => true,
        'show_in_nav_menus'     => true,
        'can_export'            => true,
        'has_archive'           => true,
        'exclude_from_search'   => false,
        'publicly_queryable'    => true,
    );
    register_post_type( 'gruppen', $args );
}
add_action( 'init', 'gruppen_post_type' );

this is the content of ‘page-gruppen.php’:

<?php get_header(); /* Template Post Type: Gruppen, Gruppen */ ?>
    <div id="sidebar">
        <?php get_sidebar(); ?>
    </div>
    <div id="main">
        <h3>Titel</h3>
        <div class="gruppen-album-holder">
            <?php if (have_posts() && the_excerpt() == 'Blauring') : while (have_posts()) : the_post(); ?>
            <div id="<?php the_title(); ?>" class="gruppen-album"><img src="" alt="<?php the_title(); ?>">
                <h4><?php the_title(); ?></h4>
                <p><?php the_content(); ?></p>
            </div>
            <?php endwhile; endif; ?>
        </div>
    </div>
<?php get_footer(); ?>