Jan,
I learned that lesson too. I broke down and purchased just about every size square they make. When I trimmed the 8 1/2" blocks now, I take that square lay it right in the middle and make sure all the angles are correct and then trim them. I think lining up all the lines in the square before you cut is the answer. Right now make a unique border or put them together in an unique pattern of your own and NEVER tell a soul. My husband loves all the quilts I have made and doesn't realize my "creativity" has been stretched on several of them. I make every quilt a learning experience and love trying to figure out a neat way to solve a whoops on my part. No one is perfect....have a great day.