I would never do them that way. You end up with bias edges on all the edges. Cut the squares bigger, draw the line down the center and sew a quarter inch away and then trim them down. The rule is to add 7/8ths of an inch but you can add an inch or even an inch and a quarter and the square them up to perfect.
Buy this, you'll never regret it, from Bear Paw Productions. She's wonderful to deal with.