Pregnancy Update! 6 weeks and 6 days Today!?

Exactly one week ago today, i went to the doctor for my first sonogram, i was 5 weeks and 1 day pregnant. The sonogram tech only expected to see a gestational sac and yolk sac but the doctor felt that she should have seen a fetal pole and heartbeat. The doctor suggested i scheduled a d&c for the next day but i denied her. I did go today for another sonogram and today there was a fetus with a heartbeat of 148. I am due December 15th! I thought today i was 6 weeks and 1 day but my measurements i am 6 weeks and 6 days!