Fold your backing in half and press. You only need to press at the edges; not all the way down the entire length. Now fold again and press so that you have a fold line in both the horizontal and vertical directions. Do the same to your quilt top. Cut your batting a little larger than the top and the back a little large than the batting. Using the folds as a guide, you can line up the quilt top to the backing to make sure it's all straight. If you don't like the idea of pressing folds, you could just mark the center points at the top, bottom, left and right with a chalk pencil.