Please continue with your beautiful quilt by all means. In her books Mary Ellen Hopkins talks about "PPM" your personal private measurement. She goes on to say that as long as you use the same machine, and continue to keep the same seam allowance in all your blocks your quilt will be fine. It's all about being consistent. After you finish this beautiful quilt if you want to go ahead and figure out a "perfect 1/4 inch seam" then do so, otherwise continue as you are doing. From my perspective you're doing a fantastic quilt - you go girl.