I would also go with 2" cut strips, which would finish at 1.5, with a 13.5" block. To me this measurement makes sense because if you look at the white sashing, it's about twice the width of the small squares in the main block. The 3" finished sashing (3.5" cut) also lets you make a reasonably sized 9 patch cornerstone: each patch would finish at 1" (cut the strips at 1.5").
If you had 5 blocks across and 6 blocks down, with sashing between each AND around the perimeter, the quilt would measure 85.5 X 102. you could add borders if you want it bigger.