As a general rule I try to use the same ruler throughtout the cutting process. Once the blocks are all pieced as long as they all are the same it doesn't really matter any more. Relax and go ahead and put the blocks together. If you have sashing or borders make sure you cut them to fit you blocks or quilt top size and you'll be fine. Another thing I thought of about your size differance, have you double checked your 1/4 in. seam allowance? Not all 1/4 in. feet are totally acurate.