Dumb question here

When I had my dating scan baby was measuring 2 days behind my lmp. My doctor kept the due date based off of lmp but I’ve been tracking baby’s growth based off the measurements . At my 12 week appointment baby then was measuring a day ahead of what the measurement was at the first scan. But then for my 16 week appointment I had on the 5th the nurse used the lmp measurement . So now I’m confused if I’ve been tracking growth wrong . I know these variations are normal and since the due date has never changed it doesn’t really matter . But I’m just curious now if I should be tracking based off lmp / due date and not 2 days behind like I have been .