How does that work?

Hi!
I'm going by my last period and am 10+5 weeks pregnant, according to my midwife.
Now I've had my dating scan and that lady put me back to 9+5.
If I count back from that, I don't get to the first day of my last period, but with 10+5 I do.
I've been off the pill for a bit over a year now and I've kept good track of how long my cycles are, including using ovulation tests and stuff.
At first I had longer, irregular cycles, but for the past half year it's always been 32-33-34 days, not longer, not shorter.
Am I therefore less far along in my pregnancy because my ovulation was later due to a longer cycle,
so that means my fertile days shifted?
That's how I understood it anyway