How far along in my pregnancy am i?

okay....so i went to the doctor and got a l sonogram. my baby measurements and it is 5.4cm. (i was looking on the internet and it was saying that 10 weeks a baby measures 3cm) and my baby heart rate was 153. my last first day of my period was November 22, 2010. right now i would be 9 weeks and i got the sonogram at 6 weeks. was they right or could i be further along?