The best advice I can give is to oversize your squares. Draw a diagonal line from point to point. Sew 1/4 inch on each side of the line. After you cut these apart and press, then trim them to the size needed. Make sure you use a ruler with a 45 degree line that is lined up on your seam. It seems that no matter how carefully I cut and sew my blocks never come out perfect. That is why most quilters will over size and trim down. If your pattern said to cut squats at 3 7/8, cut them 4 inches. That little bit can make a huge difference and save you a lot of frustration