I don't know if I'll be able to explain how I do mine but hopefully I can. It always seems like there is a little difference in the size of the pieces you measure check and cut but sometimes they just come out different. So, I will lay the squares further to the bottom because they are going to be flipped and pressed up. I press very carefully as to not stretch or wrap the fabric because it's on the bias. Then when I trim my block I make sure that there is a 1/4 inch to the point.
You could also try cutting your squares a smidge bigger and then trim away the excess.