First ultrasound- 3 weeks behind?

I had my first ultrasound yesterday and based on my calculations I thought I was around 9 weeks.

My ultrasound measured at 6ish weeks - there was a gestational sac and yolk sac but no baby.

My midwife said I could have ovulated later then I thought since I didn't necessarily track my cycle. And if that's the case and I really am 6ish weeks, the ultrasound would be on track with the gestational age.

I'm a nervous wreck and have been crying non stop.

I don't know what to think. I never had this with my son so this is all new to me.

I'm obviously thinking the worst but am trying to be hopeful while preparing myself for bad news.

I have a follow up appointment on the 17th for bloodwork and another ultrasound.

Any advice or experience with this?

***note I got my BFP on July 30th***