mine is 2 blocks x 3 blocks..............so I am going to keep the inner border at 1 1/2 inches and make the adjustment with a yellow or possibly black 'keystone' in the center of each border strip.....or maybe green....hummm...will audition the colors first.....or a second inner border.....hummmm thinking....
or I could use some of the black and white checkerboard fabric for the inner border if it is printed on grain, actually have it in two different sizes of check......or not...have to consult the 'buzy' meter.