Originally Posted by
bearisgray
I would use a pencil and just mark the 5-1/4 inch square in a corner and cut around it.
Then either scissor cut it out, or rotary cut on the lines.
This is what I was gonna suggest also. But like Dunster said, if it needs to finish at 5" square, it should be cut at 5-1/2" instead of 5-1/4" sq.