I may not be able to add any other thoughts or recommendations to fixing the problem and so many good ones are already offered. What I can add is encouragement that you will get it worked out and your quilt will be lovely. Keep in mind only you will notice the discrepancy in the quilt. It is so beautiful to start with and it will be when it is finished. Also know that just about all of us have been where you are now. I just finished a quilt that I pictured here a couple weeks ago that was off by 2-3" so I cut off half a block to make it right. I doubt very much anyone who saw this quilt would notice it without very careful examination of the quilt. Yours is such a beautiful quilt that all of us will only see the beauty of it as we do now.