Well, if it really bothers you you can try ripping the center seam again so you have two halves. Then carefully pin it, making sure to line up each intersecting seam (you can also use a dot of elmer's school glue). Then when you go to resew it, start at the center and work out to the edge. Then flip it and do the other half. Sometimes that helps it lay flatter. I really think an inch to inch and half cup will quilt out though. Here is a link to mine:
http://www.quiltingboard.com/picture...lt-t22341.html
I hand quilted it 1/4" from the seam inside every diamond. But I have also seen machine quilted ones quilt out nicely as well.