Confused on dates

Trying not to ask silly questions but I wondered if I could take my one silly question now?

To set the context I am in the UK and understand the prenatal system in the USA might be slightly different.

Anyway according to nurture I should be 10 weeks 4 days (from LMP) today but I had a ridiculously early scan a few weeks back because I was bleeding.

The ultrasound technician said there was a healthy pregnancy but that I looked like 5 weeks not nearly 7.

So I updated nurture to reflect this.

Fast forward roughly 4 weeks and I had my first midwife appointment. I told her about the scan and that although her prediction would put me at 10 weeks 3 days I was actually more like 8 weeks and 6 days.

She wouldn’t take my dates and insisted I was 10 weeks 3 days and put me in for my 12 week ultrasound in 2 weeks!

I’m panicking as that will make me only just nearly 11 weeks (10 weeks and 6 days) but she said the scan needs to be done during the 12th week to screen for down syndrome and other abnormalities.

So my question, is it possible to be a week out as the scan was so early or when I get my appt should I push it back?

And how pregnant am I actually ??