When calculating the piece sizes, start with the finished size you want when the block is sewn into the quilt. Then once you know that, add on the seam allowances
Finished size = 2"
3x3 for a nine patch, each piece needs to be 1/3 of 2" => 2/3"
Add on seam allowances, 1/4" for each side => 2/3" + 1/2"
Which means each of the nine pieces need to be 1-1/6" ... not easily measured!