Looks like you would sew the 2 1/2 inch strip to one side of the printed fabric block and then sew a 2 1/2 inch square to a second 2 1/2 inch strip to equal the measurement of the print fabric block + the added 2 1/2 inch strip. Here are two videos maybe that will help:
https://www.youtube.com/watch?v=9_6AEKTi6r0
And here is the other....
https://www.youtube.com/watch?v=4KkpbFKBaKA
Good luck!