Went to ultrasound and dating is WAY off

So I had an ultrasound today, I was supposed to have been a little over 10 weeks. When she did the ultrasound, she said I’m only around 8 weeks 5 days. She told me it could have been a mistake in the dating since my periods are irregular, which I guess could make sense. Before this last period, I hadn’t had one in 3 months.

I just feel weird about it, she said the heartbeat was 170 something and that it was “perfect.”

I guess I just need some reassurance that the baby is okay? 😭