Square it up and give it a good pressing. A border would give you a straight, seam free edge to bind, but you could also just sew a line all the way around the outer edge to keep your seams securely. Put borders around your backing so it is a couple inches all the way around larger than the top. Your batting should be a bit larger too. When you put the (sandwich) together the top should be centered on top of the batting/backing, so your*panal* backing should be fine. As for {shifting} that should Not be happening. You can use any number of methods for basting your sandwich to keep it from shifting. There is fusible batting, spray basting, glue basting, pin basting, or thread basting. Which ever method you choose should be done to keep your quilt from shifting while quilting.