Someone on here taught me a neat trick especially if you piece your backing. Leave part of the seam of the pieced backing open. That way you sew all the way around your quilt and turn it inside out from the backing. Blind stitch the backing closed and voila!! your side seams are all straight and even and it looks great. I've done this even when I didn't have to piece the backing--just cut the backing, sewed it 1/3 down the seam, left 1/3 open, then sewed the bottom 1/3. Hope this helps someone.