Originally Posted by cmbdiesel

Speak directly with the owner of the shop, preferably in person, with the car.
If he/she does not agree to make the situation right, call the insurance company and report the issue, then call your DMV and file a complaint against the body shop.
You can do these things while at the body shop if you like, might get a quicker response.

I can't imagine a situation where the shop wouldn't want to effect minor adjustments to your repair in order to remain in good standing with the customer and the insurance company.

Additionally, I think I would take the tack with the owner that 'there may be undiscovered damage' which has resulted in this problem, rather than 'your shop f**ked it up'.....
If it were just a light tap on the fender, It shouldn't have done much beyond the sheet metal, but it may have bent a support which was not covered on the sheet. He gets to make a few extra on the new part and labor, you get your car fixed, everyone is happy.

Also might be worth checking with the insurance company to ensure that the fender which was installed was actually OEM. Your problem may be a POS chinese fender. I really can't imagine how you got them to write for a new OEM fender in the first place.... very hard to believe. Keystone or used would seem to be the only rational choices for a car of that age.