Unsure of what is right ..

Shelbi
I was informed that if a sono is done too late it could be inaccurate of due date, lets say after 11 weeks. How is this possible? I think that I am two to three weeks further than said by my body and documentation. My husband believes so too. My dr is not listening to how I feel and making me feel like I'm speaking out of spite. I am really not doing this. If their measurements are correct that's great cause either way baby is coming. They just made me quite discouraged.  
Below is supposidly measurements of an 8 week 6day baby. Which not thirty minutes before I had a pelvic exam and was told I was 15 weeks. This is quite a jump from either estimation on how far along I am with baby. 
Based on my calculations and what I saw not in pictures but during the "quick" sono was a 10 weeks baby. I went for a second opinion and other reasons but was only informed of what was transferred and not based on new information.  No pelvic exam was done. No hcg levels were checked at either hospital as well.