This is exactly what I would do. One reason to do it this way is because of the folding - If you fold a quilt in half and that's where the seam is, it puts a lot of stress on that thread. It also "pulls" on both sides of that single seam when you have a center seam, but if you use the full width in the center and two half-widths on the outside, there is very little "pull" on the seams when you handle the quilt while making the bed, sleeping, hanging it to dry or folding it for storage.