It sound like you might have got something like I got. I got the large matt to go on top of my cutting table that I also bought at JoAnn's. Then after a few times cutting I couldn't figure out why all of my new rotary blades wouldn't cut; I tried different ones. Then I tried them on a reqular cutting matt and they cut just fine. The large matt isn't self healing so after a couple of times cutting it won't cut on that area again.