No heartbeat on 6 th week

Dear

Accouring to my last period which is 3rd Dec, when I had a hospital visit three days ago; I was 6 week and 6 days. I had ultrasound and it says I am 6 week and 2 days based on size of baby.

Anyways the doctor did not find heartbeat at that time. She said we shall wait one more week.Is that ok ?