Help me please

I had to go to the ER yesterday for bleeding and the doctor believes that I’m having a threatened miscarriage because they couldn’t see the fetus on the ultrasound. But then she checked my cervix and it was closed. I’m only 6 weeks pregnant so could it be too early to see it? 😢 I hope the doctor was wrong!!! My levels are also kinda low so I have to my obgyn and get my blood drawn again.