How thick were the flatheads you used? I used flatheads that have pretty thin heads and are about 1/4 inch wide. I also inserted them in the thinner tech detailed side and slid them around. Just curious but what was your process? I don't understand how you destroyed the shoulders that badly. You could still fix them. Especially if you are handy. They could be sanded using decreasingly finer grit then heated with a hair dryer to remove the rest of the marks.