So far, your plugin is working great. However, I found a bug where anyone can create a duplicate post.
This is how I replicated the error:
Go to :yourdomain/wp-admin/admin.php?action=duplicate_post_save_as_new_post&post=POST_ID
IF the user isn't able to create a duplicate, it gets a permissions error but the duplicate still goes through and is created.
Would you be able to fix the bug please?