Hate to say it but a cover doing that is kind of on you, not the cover. They make breathable ones for exactly this reason and the cheap waterproof ones basically turn into a sauna when the sun hits them. Leaving it on for 3 weeks without checking is the real issue here, water has to go somewhere and trapping it against the paint was always gonna end bad. Spotting might even buff out with a mild polish and a pad, so dont panic yet lol.

Ever check if that little screw backs out cause the bracket's bent?

20-30% illuminated" is the sweet spot, that terminator shadow is everything.