First. Ultrasound .. Im really confused, Help

So i went for my first ultrasound yesterday... I didn't really went for that, but i had extreme headache and i needed to get my blood pressure which was high.. So my dr wanted to do ultrasound to see if everything was fine... According to my calculations, i was 6 weeks 6 days yesterday.. But ultrasound showed me at 7 week 6 days (which isn't possible cause my last periods first day was 29 September) .. My dr also scared me by saying its weak, and idk what tht means, i couldn't eat much cause of morning sickness and i cant eat all the things i loved before nd craving for fruits..

Anyways.. My question is tht Did this ever happen to u.. Tht your ultrasound showed your gestational age about a week older.. Acc to tht ultrasound im 8 weeks today but i know im Only 7 weeks.. Anyways.. I guess it's better than being behind than Ahead.. Lol.. But im really confused.