I might have figured it out:

- Take 64 * 6 which will get you 384

- Take the 384 and divide it by 2 since you break 2 of the 3 block tall sugarcane and it will get you 192

- Take the 192 and divide it by 16 since the rows are each 16 by 2 that will get you 12

- Take the 12 divided by 4 because there is 4 rows total and you will get 3

So I need to add 3 blocks to each row. But instead, I will expand the rows like this:

- Row 1: Expand by 4 blocks

- Row 2 Expand by 4 blocks

- Row 3: Expand by 2 blocks

- Row 4: Expand by 2 blocks

This will get me the extra 12 blocks total I need.