Empty Sac 5 weeks 5 days

Hey everyone! This is my first pregnancy and I wanted advice. I went in for an early scan last week and I thought I was 6 weeks. Turns out my gestational sac was measuring at 5 weeks 5 days and it was empty. There was no yolk sac or fetal pole. My doctor did seem a little concerned but said it’s not unheard of. Do any of you guys have similar stories? Looking for any insight here at all. I have a follow up next week.

HCG- 41.8 on 10/14

7800 on 10/26 (4 hours after 6 week ultrasound)