MimiSharon, this is has happened to me more times than I like to admit.
A regular 3" x 5" file card has lines 1/4 inch apart. Run it through your sewing machine to check the accuracy of your 1/4" foot.
I have found that my 1/4" foot is just a scant bit big (but big enough to throw everything off) so I always shoot for a "scant" 1/4 inch.