Had my 10 week ultrasound, turns out I'm farther along

Alison

So I went in for my 10 wk ultrasound today, and they said I'm 11 weeks 4 days. I'm confused because I charted everything and did ovulation testing and it's basically saying I got pregnant before my last period. Has this happened to anyone else?

Also if the placenta is straight back, does that mean boy or girl?