The math of adding seam allowance for a triangle is 7/8ths an inch for the point instead of our usual 1/4.
That means when you cut a square on half on the diagonal, you basically need an inch bigger piece to make the square.
Depending on how far you've gotten in slicing and dicing, you may want to trim your solid squares down to the size of the HST.
Hope that is fairly clear and/or helps your quandry!