Here's the back of the block. The seams are pressed toward the darker fabric or the unit with fewer seams to cut down on bulk. Seams that meet are pressed in the opposite directions to help them meet correctly.
Where the half-square triangle units are sewn to the square, notice that the seam goes through the "x" where the seams of the triangles meet. This helps make the points sharp and not cut off.
Notice in the sixth row where the seam is clipped in the middle to allow the seams at the points to be pressed so the "x" of the seam is exposed for sewing through. Sewing through the "x" assures a sharp point on a triangle.
Click here to see the front of the block.