Did this happen to any of you??

So I went to my doc appointment since I just found out I was pregnant a week ago. They did a vaginal ultrasound but they didn’t see a sac. The nurse practitioner said it can still be too early. They said I was 6 weeks and a day but they may have the dates wrong and I can be earlier than they think. I go back in a week but I can’t help but to worry.