I have an easier way to make those pesky 1/2 square triangles. I use the tube method. I cut a 3" strip of each fabric, put them right sides together, then sewed down each long side using a 1/4" seam allowance. Then I took my companion ruler, which has a 90 deg angle, and put the point of that angle on one of the seam lines, making sure the other seam is straight with the markings, then cut on each side of the 90 deg angle. When I took the "point" apart, and pressed open, I had a 1/2 sq triangle piece that I trimmed to 3-1/2". Some didn't need much trimming, though.
to make the 2nd and succeeding triangles, you flip the ruler over and put it even with the cut edge. then cut another one, etc etc.
I'm still working on the B & C triangular pieces.