I've been busy cooking and cleaning for Thanksgiving so hadn't been back to see if I had any responses to this post. Thanks so much for all the great ideas. I tried leaving it out in the sun and it didn't take out the warp but hadn't tried the hot towels, maybe I'll do that first. I love the idea of making a rotary cutting mat, the cookie sheet idea, making templates, using under the sewing machine, etc... So many smart, resourceful and just downright friendly people here, thanks and have a great Thanksgiving with your loved ones.