When using the Go the selvage edges have to be facing you when you cut to insure accurate cuts and no stretching of the fabric. The mat may be pulling the fabric so adding a piece of paper on top of the fabric and then the mat will prevent that. I usually cut four layers at a time. If the fabric is lightweight I fuse a featherlite interfacing to the fabric before cutting no matter if I use the Go or the rotary cutter. I do this for any bias cuts too.