Cut two squares that are 2 3/4"
Sew your 9 patches to the 2 3/4".
I highly recommend you continue to mark your 1/4" seam allowance. I did because I wanted to make absolutely sure my seam allowance was spot on.
I only did half of the block to show you. And remember the outside blocks are going to be bigger than the center because of the seam allowance.
Hope this helps.
Recap: cut strips 1 1/2"
trim to 1" from seam
cut sections at 1 1/2"
trim to 1" from seam
trim the two outside strips to 1" from seam.
You should have a square that is 2 3/4" add to 2 3/4" square = 5"