I’ve been going insane because of this drawing!

It’s a commissioned piece and I’ve been working way too long on it! I’ve already decided to not charge the customer because I HATE the drawing. I literally keep seeing things I don’t like but I can’t seem to manage to fix them.

Even my dad said it was a lost cause and that I would rather have to start over, but so much work would be lost…

Any advice on literally anything would be appreciated!!! I’ve been pulling my hair out over this drawing :(.

The second picture is the reference btw! The bridle obviously still needs more work like highlights etc. My frustrations are more centered towards the coat of the pony.