Sometimes the more you work on it, the worse it gets. Leave it be after trying all those things. The only thing I've ever found that took out old, set in stains was RetroClean. Pricey, but worth it. For this one, let it go. Your friend will understand! Or make another and keep this one...it is so beautiful and there's so much love poured into its completion that it just needs to be used. After awhile, you won't see the marks, just the overal beauty of a job well done.