i would pin the ruffle or pleated strip to the completed front, all the way around, raw edge to raw edge. lay it on the floor, face up. lay backing face down on top matching sides and corners, then batting. trim the batting close. sew all around, at least 1/4" but up to 1/2" being careful not to lose any points on the quilt top. leave an opening on one side of the quilt large enough to reach in and pull the quilt rightside-out. this is called birthing. when the quilt comes through the ruffles will be placed correctly. using an invisible stitch of your choice, close off the opening. i would then topstitch through all the layers 1/4" from the outside edges. using this method, tying off is the safest way to put all the layers together, but you can 'tie off' with machine embroidery or machine Xs. tying off with buttons is also used.