Confused, is this normal?

Hello all! 
Today I had my first sono! I am around 9w6. We were told the baby is measuring 6w3 which she said would put out conception at February 3rd. I got my first positive test on January 29th, got into a first doctors office on February 2nd and put me at 4 weeks. I know we tried to conceive on January 12th and can't think of any other time after that day that we would have had a "moment". She also informed me that the placenta has not formed. Has this happened to anyone else? We are very confused! But we do have a video of the heartbeating!!