First ultra sound time frame

Cristine • First time Mom, with 4 step kids. Can't wait to meet my baby girl in March 💕💜💕
My dr said I cant get an ultra sound or blood work till in 10-13 weeks. Well I go on Monday and I'll be 9w2d (according to my PCP) I see everyone post pictures of their ultra sound at 7,8,9 weeks. Why do I have to wait? And to make matters worse if I really am only 9 weeks I have to wait a month to go back and that puts me at 13 weeks.