I did what eparys did ~ marked it very lightly on the backsides, just the corner intersections ~ then I stopped just short of that, which gave me more wiggle room to get the next ones lined up and laying perfectly flat. I am doing the carpenter's wheel/star, which is 100% y seams
I probably didn't need to, but I also took both threads thru to one side and hand-tied them in a boxknot so they could not lose a stitch at a pointy-point... just my peace of mind before it is quilted, if that makes sense.