Confusion with current gestational week.

I am facing the following issue-: My LMP is 23rd June which makes it 11 weeks 3 days today. My first sonography showed 7 weeks 6 days on 14th of Aug which makes today as 12 weeks. Today I went for the NT scan thinking I am in my 11th/12th week and it showed 13 weeks 2 days. Apparently the radiologist told us that the computer software measures the length of the child and calculates the week which is supposed to be most accurate as compared to the LMP and even the prior sonography. He mentioned as I am in my 13th week, I may not be eligible for double and triple marker tests which I had planned to do. My husband is 6.1 feet while I am 5.10 feet. Can this cause the child to be taller than usual which is causing the software to make an incorrect calculation. Plz help.