I think your quilt is lovely. My first quilt ended up in the wastebasket..... it was that bad. I'm sure your quilter will be able to finish your quilt no matter which way the backing is stitched. And I wouldn't worry that one side is 1/4" longer than the other..... You aren't entering it in a quilt show and when it's on the bed, no one will know.
Great Job on your first quilt...... Upward and onward!!