Well, that was a bit of a surprise, as I drafted it out it is much happier as 17" blocks with a 6" flying geese unit. The sashing would be 3" instead of two and it should finish out at pretty much the correct size....
For 5 minutes of work it's what you get!
Edit: for a similar look and less work, make the 12" (finished) flying geese block (6" strip plus 3" frames), and alternate with solid 12" squares (finished, 12.5" cut). In that case you would set diagonally. As drawn it is a straight set.
Please note: Measurements shown on the block are finished sizes, not cut!
Last edited by Iceblossom; 10-22-2019 at 12:48 PM.
Reason: Made clarification on cut/finished size