So confused

I know 100% that the first day of my lmp is feb 18th and I ovulated around 1st/2nd March which would make me due on nov 25th and I’d be around 17 week mark. (I keep a diary plus remember the day well as I was about to go out to a important lunch when Mother Nature called ☹️)

But when I went for my dating scan my dates are wrong

They scanned me and said I was 12 weeks exactly on may 30th which would make me due dec 12th and I’d only be around 14 weeks 🤷🏼‍♀️ how can it be that far out