Body plastic is made for thin applications of up to about 1/4" thick at the thickest. Less is more so to speak. Having said that I worked for a used car body shop in the '60s and some of the stories I could tell.
One '63 Impala ended up with inches (yes plural) thick plastic in one spot. Of course the idea was to make it look good long enough to sell it. Once it hit the street all was good.
You need to get all of the old plastic off and see what you have underneath. What is living under will tell you how to proceed, whether some straightening will do the trick or if panel replacement is the fix. Good luck.
