I fell into a similar trap with this quilt
http://www.quiltingboard.com/picture...g-t219340.html
I had always planned to do one off-center strip down the back but when I'd done it I realized the back wasn't going to be wide enough. I had to go back and cut it open, add more strips, and sew it back together to get a wide enough back. In the end, I liked the back a lot but I certainly hadn't planned to do it that way.
