Ultrasound shows different due date

Sara

I had my LMP ON June 22, ovulated on July 14 found out on July 20 that I had a positive pregnancy test. I have pcos so I'm happy I got pregnant to begin with. I'm just confused on the due date. The ultrasound showed a gestational sac only and she thinks I'm 2 weeks but by my LMP I feel like I should be around5 weeks. Can someone help me understand please.