You said that quilt is square blocks. Perhaps your seam allowance issue resulted from where you joined your rows or columns. If that is the case then you maybe be able to do what I have done in the past. I have been able to just correct a narrow seam allowance by stitching down the seam again.
I think that if your quilt is large nobody but you will ever notice that it is out of square by a 1/4 inch, though.