in the gallery/wide_slideshow/index.php file, checnge this line:
$gallery = get_gallery(get_mediarss_url('gallery=' . $pg_id . '&thumb=62c&full=995c'));
to use a gallery size that will fit the header area, like 782c:
$gallery = get_gallery(get_mediarss_url('gallery=' . $pg_id . '&thumb=62c&full=782c'));