The pictures of this look so puffy that I had to go look at the quilt again. It actually IS very flat and straight and the quilting doesn't stand out like that! The border is a print from the fabric line that I mitered the corners on. I wouldn't have even attempted to do this on a quilt that wasn't square, as in the same measurement on each side (and square). I will be cutting off the edges back to the red (the outer white cut off) and binding it with the same red fabric.
This is the corner detail on my quilt and one that someone posted a pic of one they had seen with the same fabric... which is why I would not have done this on a another sized quilt.