is this a pre-ruffled ruffle? if so you can just make a narrow binding to cover that raw edge and lay it right on top of the binding and sew it on with a decorative stitch. If you are making the ruffle, but make the edge part a bit wider and fold under and then sew onto the quilt. When I made a quilt with a ruffle, I used a pre-ruffled ruffle and it had a narrow binding on the edge so it make it easy to sew down. Otherwise I would have made the edge wide enough and just turned under before I sewed it down.