I ended up with a mixed block version (long story) so I have a top with both blocks.
The instructions tell you to make 2 cuts, each direction evenly spaced to make 9 sections. I decided that by trimming my blocks down to 12 inches, I could use 4 inches as my cutting mark. That was easier than trying to figure out how many inches 12 and 5/8 divided by 3 was. It also meant my blocks would be the same size.
The details I will be showing are for trimming down your block.
My ruler is 12 1/2 square so I needed to be careful that I was lining up the center with the 6 inch mark vs. the 6 1/2 inch mark.
Notice how the “6” is in the center of the pinwheel, with the horizontal, vertical and diagonal lines match with your ruler lines. Trim the 2 sides at the 6 inch marking. If you are using a 12 inch square ruler, turn your ruler and block and trim the edges in the same manner. If you have a 12 1/2 inch ruler as I do, turn your block but not your ruler.
This will give you a square 12 inch block.
Enjoy the Journey, Jackie