I added some lines into your code to fix the orderby meta_key feature.
around line 45 in index.php I added:
$instance['meta_key'] = addslashes(strip_tags($new_instance['meta_key']));
AND then around line 100 you had the wrong key for the "order_by" index
I changed to this:
if(($instance['orderby'] == 'meta_value' || $instance['orderby'] == 'meta_value_num')