I have used Fray check before, and it leaves a slightly harsh finish, or it did years ago when I used it. Don't know about these days. I gather you are doing needle turn applique? I do machine and am tempted to try the method of making a backing for the applique piece, then turning it so there are no raw edges, then sewing down with a blanket stitch. You can use a variety of backings, Heat-N-Bond lite and iron it on, or a thin Pellon or the same fabric as the applique piece.