Had to google Granny Square Quilt: https://www.google.com/search?hl=en&...50.DG8ojca3c4k

Looks like most of them have different centers.

My advice is to audition the center piece. Cut out enough squares for several blocks, set them out on a design wall (or in my case, the design floor) and use a different fabric in the center for all of them, then take a picture and look at the picture.