Originally Posted by sushi

You could put the squares together with lattice strips to make the backing of the quilt. Since you have 20" to work with horizontally, you could put a 2" (cut 2 1/2") vertical lattice strip between the two columns of squares. Since you have 24" to work with laterally, you could put a 2" (cut 2 1/2") horizontal lattice strip between the two rows.

This still leaves you with 4" more vertical inches. To fix this, you would do one of three things:
1. Trim 4" off the top of the original panel (front side of quilt), thus making the quilt square.
2. Add 2" (cut 2 1/2") borders to the top and bottom of the back.
3. Increase the size of the horizontal lattice strip to 6" (cut 6 1/2"). (This is my least favorite option.)