When I use prequilted fabrics, I do a French seam - first put back sides together, stitch a very narrow seam, then fold right sides together and stitch just outside the edge of the seam that is encased in the seam - hard to explain, you can google it and see tutes - it will keep the edges from fraying, and leave you with a nice clean finish. Another alternative (but more time-consuming) is to bind all raw edges with bias tape, like you would bind a quilt, except you can SID the second side when you turn it, then just make a regular seam - either way works.