Man, that’s nasty.
It couldn’t hurt to talk to the shop. Maybe the regular guy was out that day and some goofball did it just to get it out the door. Maybe they’d be willing to send it to somebody who does know what he’s doing. I wouldn’t hold my breath but it’s worth asking.
You never know till you dive in but I doubt #83 will even come close. Just looking at it my first thought is
Meguiar’s #3000 paper followed by #85 Diamond Cut with a wool pad then the #83 with a foam pad.
Start with a small section, 1’x1’ and see what works.
PC.