Plastic cap on top of my bed is warped
 

I have a 2001 short bed, step-side. The bed has a wide plastic/vinyl cap that protects the top of the bed from being scratched. It has started to warp and look wavey. I have put a couple of rivits into it. The rivits work well and pull the cap back down but then it warps a few inches away.
I have seen this on alot of Chevys and it just looks crappy.
Any advise will be apreciated.