Givio: I haven't cut any more strips yet. I did think of adding matching rectangles to one side of the 'square' but decided to wait for the next clue.
I really appreciate the ideas of how to fix it. It measures 18 1/2 by 17 3/4. I bet it will be a while before I mess up my seam allowances again.
I love that you have a human calculator.
Connie