Due date confusion

Francesca • Mommy to two amazing little boys!!
I was first told that based on my cycle, my son is due January 15. Then, after our first couple ultrasounds, they changed his due date in the computer (without actually telling me) to January 12 based off of his measurements. I had my 20 week anatomy scan today and the tech said that based off of measurements he is due closer to January 9 now! Which one should I go by?!?!