Help, I need some advice...

Hello all, I just need a little bit of advice. So here’s some back story, I got my first positive test on Oct 13. After calculating from the first day of my last period this gave me a due date of June 18, 2019 & at the time I was 4 weeks 4 days. Fast forward, today i would be 8 weeks 2 days but I went to the emergency room because I’ve been having some really heavy bleeding the past two days and just wanted to make sure things were okay. I go though a full examination and have a ultrasound and when they come back with the results, everything is ‘normal’ (I hate how vague they are in the emergency rooms) but they told me I was 6 weeks 3 days.

Is it possible that I could have been that far off? I have a clockwork like cycle so it’s honestly blowing my mind that I’m not as far along as I assumed or could the ultrasound tech have possibly not gotten good measurements?