Which due date would you go by? Doctor said one thing but the test said another?

I went in for a sonogram and i was suppose to be 11 weeks. They did a test to measure the fluid behind the neck to check for down syndrome. Ok well i can view all results online and they said with the calculations on that day i was 11 weeks 6 days. So my question is would i go by what the doctors office said i was based off lmp or what the people running the test concluded. It's a 6 day difference. I know it's not much of a difference but that would put me into my second trimester which i've been waiting for so i can tell everyone.