You'll find that you can make a much neater-looking edge by melting rather than using fray-check. Get a small, flat piece of metal (I use a rectangle of aluminum flashing that is about 1/2" wide by 1 1/2 " long. Hold it with pliers and heat it up with a torch (over a stove eye woudwork). Press it to the cut edges and they will melt enough to never unravel...and you get a dead-straight edge every time.

Bill