You probably need to open up the sock so it lays flat, then fuse it to a stabilizer (I would recommend fusible nylon tricot -- less expensive if purchased online from a drapery store, but also available in small packets at JoAnn's). Only then would you want to cut a square. I would experiment with a sock, as you may want to staystitch before cutting a square. For example, if you want a 2" finished size square, you might want to stitch a 2.25" square in the sock before cutting it at 2.5".