Patti,
You should have started with a 24 inch centre block (unfinished), and added a 3 inch border to each side.
24 (centre) + 3 (left border) + 3 (right border) would be 30 inches (unfinished).
The next round is to add 6 inches to each side, so 30 + 6 + 6 is 42 inches unfinished.
Or is the problem that the block you've been sent has only a 1.5 inch border each side, making it 27 inches? If that is the case you probably need to alert Judy for advice.