6 wk 6 day no heartbeat

Went for my first ultrasound today and  I measured 6 wk 6 days. The tech didn't say a single word during the ultrasound. She did abdominal and then she said she wants to do transvaginal. There was no heartbeat. I'm pretty sure of that. The only thing she said was that my doctor will get the report in 2 business days. After that she left the room saying have a good day. I was able to see the sac and baby in it which was as small as a seed. Now I'm upset. What if I'm having a miscarriage. How long should I wait to call my doctor.