There are only a few shapes that can have a problem if not cut on grain. The 5" square is one of them. What you can do is cut a piece of paper, then compare a scrap fabric cut to the paper cut. Maybe cut the scrap purposely on the bias or any which way. If the fabric cut matches the paper cut, you are good to go.
Edit: If you need really accurate fabric cuts, or if your fabric cut doesn't match the paper cut, you can starch the fabric heavily before cutting to get more accurate cuts. It's not necessary for most cutting, though.
Last edited by Prism99; 01-07-2017 at 01:33 PM.