are you able to determine why they are not coming out right? if they are always a bit too small maybe you should cut your strips 1/4" wider than needed, make your 4-patches- then line up your ruler & trim each side to make the perfect size. that seems like the easiest solution beyond figuring out what the problem is & fixing that. are you sewing with a 'scant' 1/4" seam? often the easiest way to fix is to cut larger & trim to size.
good luck