Hi everybody, I too ended up with warped cutting mats when we moved 7 years ago. But someone told me to lay it outside on my driveway when the sun was out. Sure enough, it heated up and was flat again. Then, I took it inside and put it on my cutting table and left it over night. Next day, I could put it away "properly". This saved all my cutting mats. You might try it and see if it works for you.
PennyG