Twenty twelve – Add custom fields to a custom post type

How can I add custom fields to a custom post type in twenty twelve. I have been able to do this in twenty eleven by creating a single.php and add a line of code <?php get_template_part( 'content', get_post_type() ); ?> then I would create a eg content-movies.php and in there I could add my custom fields. When I try the same technique in twenty twelve the added content repeates its self in the footer area or at the bottom of the post. Does anyone now how to add custom fields to a custom post type in twenty twelve.