If you cut thr tabs of of those parts, then, using a Hard Rod with a Ball shape, you will be able to form them into rounder surfaces. When gluing times comes, use thin (in thickness) pieces of paper to glue them together, before the glue completely drives, make sure the seams are cut so no black lines remain, and use the tool to finish rounding them from the inside, and that should give you some pretty good looking fenders.