Origami -- I hope to find out a definitive answer today, but when the clue was first released, my count of the number of strips needed was less than the original amount of yardage quoted. Some of it can depend on how wide your fabric is, sometimes being able to cut just one more piece per row makes things come out way better, other times you still need more. Count up the strips cut for the sashing and don't forget the extra strips cut for that inner border. Also notice that the border is wider than the sashing!
Keep in mind that you can cut wide bands and then slice them into narrow rectangles, or if you are just a couple pieces off, you can cut a narrow strip and get a couple more pieces that way.
When I was looking at using my "splattered" aqua, it is a bit short on the yardage but it seemed to be enough. I also thought about ways to extend what I had, so that the inner border doesn't have to match the sashing. Or, I considered using a different color of sashing just around the corner blocks or going 2 blocks in (on the diagonal) -- gives sort of a medallion effect.
Been in a low funk last couple of days waiting on my 4" inches of white... is in the dryer now so maybe I should go cut my sashing and get a better answer.