I frequently have to piece fabric to have enough for the back. I buy enough for the width of the quilt including 8" (4" on each side for the quilter...or whatever your quilter needs). First I iron the fabric making sure I iron out the fold, then fold it in half (the opposite of the way it comes folded), make sure you the fabric is face to face, then sew along that line. Cut through the end you just sewed and open it up. I iron the seam open, not to one side as you do piecing your quilt so it doesn't add bulk. After it's quilted that seem will hardly be noticed and the quilting should add strength. If you have a very large quilt you may need to buy enough for the length (or width, whichever works out better), plus whatever the quilter needs and seam it with 3 panels. I can't wait to see your quilt!