After rethinking this block, I have come up with this, if you want 12-1/2 in unfinished block.. Use 11 in or 10-1/2 squares and when the hour glass is made ..... Square block up to 13-1/2 in square using the center to be sure it is square... Then you can cut 4-1/2 units for the 9 patch. That would make a 12-1/2 unfinished block in the end. I took a break and worked on a 4th of July banner this afternoon. Will post photo on different link.
Judy in Phx, AZ