If they are off really badly, you can make them wonky. Add enough fabric all around so you can square them up to 9.5 inches wonky. After they are uniform in size you can add sashings. The wonky look can end up being really cute.
If they are only off a bit, just add the fabric an square up at 9.5 (or whatever). Once the sashings are added no one will notice the difference.