I have the same problem. I will be sewing hundreds of corners squares to make the snowball block. I always seem to be a little short on the corner squares. I am going to sew a hair over the line on the right side of the line to make it the square that stays on the block a smidge bigger and then I will square it up.
Does anyone have any suggestions regarding the snowball blocks?
Sewing to the right of that line will help. Remember that the corner to corner line is the FOLD line not the STITCHING line - sew just to the outside of the line to allow for the fold of the fabric and the thickness of the thread.