I did one of these and its tricky if you're not following a pattern. According to the pattern that I used, the end pieces were cut 2x the size of the original block and then sliced in half. I know it sounds weird, but try one block and see if it works. Another way that I can think of is lay a couple of the rows together and place a piece of paper underneath and then trace the size and add 1/4" for allowance. I hope one of these help.
Love the pattern!!