Date confusion????

I went to have my 12 week nuchal scan and the lady kind of got mad at me saying that It was too early? According to my first scan I was only 11w5d, but my second scan 12w,3d. She told me that although the second one showed differently, I should always go by the first dates.... But in her reports she has said that I am measuring 13w. I'm so confused 😣