I am not an expert, there are others on this board that will have the best answer for you. As I see it you may have 2 problems going on. 1. remeasure you squares and triangles. They appear to be different. Accurate as possible cuts are very important. 2. Consistent 1/4" seams are important. I do what is called a scant 1/4" seam. One or 2 threads short of 1/4 inch seams.
Hope this helps a little:) Welcome to the board.