If the above link is the correct pattern, you would cut all your squares at 3 7/8 inches (4 inches and then trim down would be much easier). Draw a diagonal line across the back of the light fabric & lay face down on a face up dark square. Sew a scant 1/4" from the line on both sides. Cut on the line. Press open and square up to 3 1/2" before sewing into rows.