didnt see my baby at 6 weeks

I am six weeks and four days pregnant with my third, I went to do a confirmation scan and my doctor thought I was six weeks and three days at the time going from my last period but they couldn't see the baby at all only the sac. So they thought I am earlier then what the doctor thinks so they said we will stick to six weeks as of that day. I am now six weeks 4 days and will be going to do my scan on Tuesday which I'll be 7 weeks and 1 day. I am worried that I am miscarrying and that I won't see my baby at this scan :( anyone else go through this, I seen my two kids at six weeks so I'm really worried. They also did a vaginal scan but still didn't see baby I need some reassurance