I made the middle 6x6
on the light corners - I made a 7x7 square and than cut it X to make four corners.
the dark corners I made 2 5x5 and cut diagonal. I believe if I use 4x4 it would be better. Will take apart and go down to that and see.
Either way of doing the block- there is absolutely no waste and no extra fabric needed.
here is the inspiration - Square-rific by April Rosenthal. She used a smaller sized squares on her corners. and then used full triangle pieces on light corners