11 weeks 2 days help?!

Heather • 41 and 3 kids. Kids are 13, 10 and 5. One girl and two boys!
So I am pregnant with my third high risk but look at me how can I be just under 12 weeks? I haven't had an ultrasound since 6 weeks 6 days. I have one next Thursday and they will date it this time. I'm thinking I could be further along... what do you ladies think? Originally ultrasound only show ed a singleton. But could I be in for a surprise possibly? I should probably add that I am very skinny and tall.