I'd suggest cutting out a 4 1/2" square opening in a piece of thin, but stiff, cardboard. Use the opening to mark a square on the fabric and then cut. Once the first one is marked/cut, use the corners of it to exactly locate/mark the corners of each additional square. Be careful to not enlarge the opening of your template while marking the fabric. (You might have to make several identical cut-out templates if you're marking a lot of squares...) I used this method to fussy cut a circle for the center of a Wagon Wheel block and it worked really well. I could see exactly what the piece looked like before I marked it and cut it. Good luck with your quilt!