I too, left mine in the car to long and it warped. I tried everything except putting it back in the car again and nothing worked for me. I called the company and was instructed to do something I have not seen on here so far. That was to take a flat cookie sheet and put it in the freezer and lay that on top of the mat with weights on it several times. Did you ever try to put something that large in a full freezer? That was a lot of work taking everything out, sliding the cookie sheet in, then replacing the food. After doing this several times it still didn't not go flat. I was so disgusted! I make blue jean quilts and cutting a long narrow piece to slip into a pant leg makes it very easy to cut using a rotary cutter. That goes so fast that it ALMOST made me happy that it warped. Then I bought a QuiltCut 2 and my problems were solved.