If all your components are identically sized, the difference is in your seam width. A few threads off on every block will add up to inches in the end.
You can make yourself crazy and pull out all the sewing, or do it the lazy way I do.
Measure all blocks, take size of smallest. Make new seam in blocks (or more if wayyyy out) to adjust to new smaller block size. If you are committed to a certain measurement for the quilt, use sashing, borders, or more blocks to compensate. Eat chocolate and remind yourself that you are only human.