Measuring ahead

Deco

I'm 9+5 and did my first ultrasound yesterday. When my obgyn did my abdomen she said I was actually 9+5 but when she did the transvaginal she was saying the foetus seems to be 4 weeks ahead. Then she tried again and says it measures 10+6. I don't knw what to believe. How is it possible to measure 4 weeks ahead. My last period was September 5.