Common terms for this are birthing the quilt or the pillow case method.
Lay the top down, right side up. then the ruffle the ruffle is placed so the raw edge matches the raw edge of the top, so the ruffle points in. It is a very good idea to stitch the ruffle down with a 1/4" seam all the way around and deal with matching the 2 ends. Next put the backing, right side down (so the right sides of the top & backing face each other with the ruffle between. Now smooth the batting over the top. Sew with the batting down, on the same seam line you used for the ruffle leaving a gap to turn it.