In the square in a square, if I remember correctly, the triangles have a bias edge. The bias edge can stretch if it isn't pinned and handled carefully. If you square up each step before adding another round, you should be alright. I did one it wool coat factory scraps years ago. I just squared it as I went because I wanted it to be more free style than exact. It turned out beautiful and it is my main "art" piece in my family room. I hand quilted it with larger stitches due to the loose weave of the wool. Enjoy the process rather than looking for perfection.