Trying to figure out my due date.

Heather • Mommy of 💙💓💓💓💓👼👼
So I have a 27 day cycle lmp was April 2nd. According to that I should be 11+5 with a due date of January 6th 2017. Then I had my first ultrasound and doctor said baby measured exactly 12 weeks. And moved my due date to January 4th 2017. Which do you think is more accurate? I tracked bbt and including my chart and ultrasound.