First of all, is there anywhere else you could use the excess?
Second, did you take any pictures of the stainless pieces coming off so that you can go back on the manufacturer? If so, then I'd try to go back on them for the labor of the repair job and get some money back that way.
As far as your contractor measuring wrong and you buying too much, that's pretty tough to call since he is fixing someone's else's faulty workmanship!