I'm new to quilting and bought a new rotary cutter and a clear wide grid ruler wth the rotary sharpening edge to cut my fabric, but i used an old xacto knife self healing mat. After a few cuts my new Fiskars rotary cutter quit cutting fabric. Can anyone tell me what I did wrong or should I have bought a rotary mat instead of using the other one? I just assumed the xacto mat would work. Please help.