Please help girls.i need some support! Totally upset

it's going to be a long one but I would be so grateful of some feedback, as I've worked myself up so much and I'm in an awful state!

I had a miscarriage in September... since then my cycles have been lasting between 45-35 days.

So it's safe to say I am irregular/no idea when they are next due & no idea when I ovulate.

My last period was 15th January.

I got a positive test 1-2 on clear blue on the 15th February.

Given that my periods are 'off' I am not confident that the pregnancy will correspond with the LMP date.

As I had a miscarriage in sept, my partner and I decided we would go for an early pregnancy scan to clarify dates and check all was ok etc.

Going off my 'dates' I would be 7w1d at the time of this scan ( yesterday, 6th March) 2 weeks 5 days after a 1-2 on clear blue

However all that was visible was a gestational sac measuring 8.5mm x 8.6mm

She did not say how far along it was. But that it definitely wasn't 7weeks. Got to go back in 10-14 days for a re scan.

I was completely expecting to be less than 7 weeks as I said I'm irregular, but I have no idea how far along I am and if everything is progressing?

What are people's thoughts? I have rattled my brain trying to figure out possible dates based on late ovulation etc.

Could someone please shed some light.