I use a utility knife (aka box cutter) to cut mat board (for framing art) on an old rotary cutting mat. The knife is thicker than a rotary cutter blade and leaves a deeper, wider less healing cut in the cutting mat. So even if it would work on the fabric, which it probably wouldn't, it would definitely ruin your mat. You could always go back to scissors if the rotary cutter is too expensive. Many of us used them for years! :D