A QR code quilt will always be square and will work out in a grid to 25 x 25. I added the white borders around it before binding it to help the middle stand out.
I would definitely make the squares smaller. With these squares beinging 3 1/2 x 3 1/2 (1/4 inch seam allowance) the quilt ended up beinging about 81 x 81 inches. So if you make the squares 2 1/2 inches then the quilt (with no border) would be 62 1/2 inches by 62 1/2 inches.
The saying isn't going to make any different in the size because the code has orienting points in it. If you change the saying it mainly changes how many white and dark spaces you have.
When I first did the code I had "I love you George" and it had a lot of black in toward the center. I didn't like the look of it. That's another reason why I added the "!". After adding that I liked the overall look of it.
I think this is the qr code creator I used. I don't remember for sure.
http://www.qrstuff.com/
I also knew I didn't want to really use black. If I had found a pretty black that had had a neat design in it I might would have. But when I saw the blue that I used I knew it would make a difference. I'll try over the weekend to get a closer shot of exactly what I used. Both fabrics I bought I got from Joann's. I bought 4 yards of each and ended up using most all of it. Then the backing I bought 7 or 8 yards. Used 6 1/2 for the backing and not sure how much for the binding. I think I might have 3/4 to a yard left.