Need help! :o

So today I went in for an ultrasound and turns out I’m 9 weeks which by my count I should be 7weeks n some days. My due date is July 20,2018. Me & my partner planned our pregnancy n I kept track of my most fertile windows, which was oct. 24-25. N those are the 2 days we had intercourse. Im just confused on how far I am :o if someone can please explain....