I did my Boxes of strings with nothing underneath. I rotary cut all my triangles and then added strips to both sides. Since I was adding strips at an angle. I kept a paper outline beside my machine to lay my blocks over as I worked to make sure I was covering the rectangle. I did 2 rectangles, trimmed the bottom and sewed then together. Once the rectangles were sewn together matching the triangles, I trimmed the block square.