WordPress create custom XML RSS feed template

I am trying to create a custom XML RSS feed. However, my code is not quite working as expected. Here is what I have done:

In functions.php I have created the feed called top:

add_action('init', 'customRSS');
function customRSS(){
        add_feed('feedname', 'top');
        get_template_part('rss', 'top');
}

In my child theme I have created file rss-top.php which contains my template file.

I am looking for a quite simple template structure like below:

?xml version=1.0 encoding=UTF-8?
articles
    article
        titleOverskrift/title
        teaserShort excerpt/teaserd
        linkhttp://link-to-post.com//link
        imagehttp://placehold.it/100x100/image
        date19-06-2017 11:21:00/date
    /article
    article
        titleOverskrift/title
        teaserShort excerpt/teaser
        linkhttp://link-to-post.com//link
        imagehttp://placehold.it/100x100/image
        date19-06-2017 11:21:00/date
    /article
/articles

I have tried creating the structure like so:

?php
/**
 * Template Name: Custom RSS Template - top
 */
$postCount = 6; // The number of posts to show in the feed
$posts = query_posts('showposts=' . $postCount);
header('Content-Type: '.feed_content_type('rss-http').'; charset='.get_option('blog_charset'), true);
echo '?xml version=1.0 encoding='.get_option('blog_charset').'?'.'';
?

articles
        ?php while(have_posts()) : the_post(); ?
                article
                        title?php the_title_rss(); ?/title
                        teaser![CDATA[?php the_excerpt_rss() ?]]/teaser
                        description![CDATA[?php the_excerpt_rss() ?]]/description
                        link?php the_permalink_rss(); ?/link
                        image?php get_the_post_thumbnail( $post-ID ); ?/image
                        date?php echo mysql2date('D, d M Y H:i:s +0000', get_post_time('Y-m-d H:i:s', true), false); ?/date
                        ?php rss_enclosure(); ?
                        ?php do_action('rss2_item'); ?
                /article
        ?php endwhile; ?
/articles

Afterwards I have updated the permalink and then trying to view site.com/rss/top.xml

However, for some reason, it just shows the latest couple of posts like it was an archive page on my site and not as an XML file as expected. Any pointers on what I might be missing ??