Week number mix up?

Had my first appointment on Monday with my ob and they confirmed the pregnancy no problem. Hubby and I had sex 2 days ago and yesterday I started bleeding so we went back in to check on baby. Everything is still just fine! Although we did get a vaginal ultrasound. According to my numbers I am supposed to be 10 weeks 1 day today but yesterday at the appointment they took two measurements. The first one she said it looks like baby is more like 8 weeks 4 days and the next one she said it was showing 9 weeks along. Has anyone else had this happen in their first trimester?