With a heat gun, going a little bit from one side then the next, slowly shrink the sides first ending up in the center last. It will need a lot of heat, be careful to not burn a hole, or yourself. Make sure that you have the sides well ironed down, and try not to reheat the sides, that would cause them to shift. When done, it will look smoother than most guys stuff out there, because you did it yourself, and listened to some advice. Know it alls need not apply.

Have other stuff to do to, but will keep you posted.