try cutting your two squares as you did then draw a diagonal line -- stitch 1/4" on each side of the drawn line then cut on the line and flip open press. i think the precision may be a little better but i usually trim (square up) my blocks after pressing, before joining them. (to square them up i place the 45 degree line on my ruler along the diagonal then trim 2 sides, turn block line up diagonal again and trim the other 2 sides...