#1 Your back needs to be bigger than your top. And your batting too for that matter. I recommend that your back be at least 2 inches bigger than your top on all four sides. That is, it should be 4 inches wider and 4 inches longer. This is the biggest problem that I have with customers' quilts. There are many reasons your back needs to be bigger, but the bottom line is, you do not want the quilter to get to the end of your quilt, and not be able to finish because the back isn’t big enough. Here is an example of what I mean by 2" bigger on all four sides. In this photo, the back of the quilt is laying wrong side up with the quilt top centered on top of it.