Could my due date be wrong?

Megan • I'm 24 years old with a 6 year old son from a previous relationship. My fiance and I are expecting a little boy due Christmas Eve. Our family couldn't be more excited.
I'm 35 weeks tomorrow, but at my drs appointment they told me my son appears to be about 22 inches long and 6lbs roughly. I'm worried that they might actually be off on my due date but they said that I'm measuring normally...any thoughts?