Vaginal ultrasound vs a tummy ultrasound

Not sure if this is the right category for this subject but will try, so I went to the doctor for my first ob appt, and was assuming I was about 6 weeks along, give or take, thee doc brought in a regular ultrasound machine and rubbed it for a good amount of time over my belly and said that thee machine may be a little old but she cudnt find anything, my hcg levels r really high according to my blood results, she said possibly about 8 weeks so we should of seen something, I asked her if I should be concerned she said no, she just wants to schedule a vaginal ultrasound for next week to be sure nothing is wrong, I asked what could be wrong, she said possibly nothing but also possibly an ectopic pregnancy can occur and/ or tubular. Should I be concerned or is this normal, to not see much at this many weeks, my periods weren't regular so I honestly don't know how far along I am for sure. Let me know your opinions please!!