So that "divot" or concave imperfection was there prior to installing then? If so, I'd hope urethane has a memory of its original form. I'd suggest leaving it outside in a hot day (if possible?) to see if it springs back, or alternativly in a large tub/bath of hot water and see if you can massage back it into shape. (avoid using any heat source which could melt it!) Bondo will not stick to well to urethane (it may initially) but I'm willing to bet that type of filler eventually break away.