Wrong dates??

Ahime
My last period started Oct 24. My doctor estimated my due date to be July 31, 2015 (making me 7 weeks today). My blood work was normal. But I had my first ultrasound today and that put me at 5 weeks, 5 days, AND the baby's heart rate was 97 (doctor said over 120 is preferred, but this was normal for the baby's age). Is this normal? I'm worried something might be wrong.