For perfection in the triangles. I get this by using a triangle size plus seam allowance from clear plastic then put triangle over the desired place and using a permanent marker draw over the top of a definate shape in the triangle. Now two options. 1. Use as it is or 2 put on other opine of clear plastic on top. You may have to experiment with the glue.
I thought the octagon shapes were kaleidoscopes. Which when I did I lined up the layers carefully. PM if you want to know how used about 6 metres of fabric but plenty left over.