why is my homescreen crooked?

I've had my Mac for about....2 years now, it'll be 3 this summer. I love it so much. I bought a screen protector, and I keep it in a bookbook case. I left it out in my car for maybe an hour. It's about 80 outside. When I brought it in (because I remembered it was out there and that I needed it) and opened it up, the home screen looked crooked. I closed it and checked, the lid is aligned as usual, and nothing looks warped. Any explanations? Can heat cause this?