You All Can Call Me REEVES And I Appreciate The

You all can call me REEVES and I appreciate the insight.

Okay, so this is quite a dilemma of mine, I hope I can explain this well. Anyway, I met this girl in Late November/2015.

We had intercourse on November 30th, 2015 and on December 4th 2015.

I had no physical contact with her whatsoever after those dates. So, she contacts me on January 25, 2016 saying she is pregnant, and that I am the only one she slept with this whole time. She sent me picture of the test, and records of a prenatal prescription. ( I know she has had a long time boyfriend, so that was in the back of my mind, but I never ruled myself out of the possibility that I might be the father)

She had her first ultrasound on February 25, 2016 and it stated that the Gestation Age (GA) was 9w 0d. I know of the two weeks of conception, so the fetal size is 7w 0d.

If I were the father she would've been 13w 3d roughly, with a fetal size of 11w 3d. I know there are big changes that occur in this time period for the fetus that are really important for development, so the doctor would've been able to tell if the fetus was further along. Especially a gap of 4 1/2 weeks.

With this info, it would put Conception in a window from January 1, 2016 - January 11th, 2016. Now again, I didn't have any physical contact with her after December 4th.

I haven't been in talked to her since (February 10) about 2 weeks before her ultrasound (on Feb.25, 2016) that determined the GA (It was determined by measurements/length of the baby) I've gathered all of this from her posting the ultrasound on Social Networks. I also saw her boyfriend posting the U/S as well. They both seem to be joyed.

But she hasn't contacted me to tell me I'm not the father. I don't expect her to, but I'm sure she knows whether I am or not. Having discussed this with her OB/ GYN. To be certain enough it is in fact her boyfriend's.
I don't believe she was lying to me, she may have genuinely thought It was a possibility I was the father until she got her scan done.

Can a scan be 4 1/2 weeks off that early??
Could I be the Father??