Half square triangles are a bugger. I found a tutorial through Pinterest that helps make the HST's come out more square. (As long as you sew on the line.) I want 2 1/2 inch blocks. So I started with a 5 3/4 inch block of each fabric. On the light color I draw an X diagonally from corner to corner. The a quarter of an inch on each side of that line I draw a line. These are the lines that you sew on. The vertical and horizontal lines drawn on the back are cut lines. Once you have sewn all the lines and cut it up you have eight 2 1/2 inch squares.
The third picture has the first row of blocks for my 16 inch quilt block that I am working on.
