Dating and due date confusion..

My LMP was on 2/18 (Slightly irregular cycles but last 3 were all exactly 33 days, nothing too bizzare)

Got my BFP on 3/27

Yesterday I had my first ultrasound at 11weeks1day (By LMP), but tech said I was only 7-9 weeks (We went with 8 in the middle) but the dates just don't line up at all.

I would've been 2weeks2days when I got my positive test by this calculation which isn't possible! Ovulation hasn't happened and baby isn't even made then?? Let alone implanted.

Has anybody has this happen with that much of a change? Did it go back to your original date later on?

It just all feels weird to me...