How many weeks do you have to be to see your baby?

So I went to the ER today and I found out I was pregnant. They did a ultrasound and blood work. The doctors come back and told me that they didn’t see anything in the ultrasound. He said maybe i am to early in my pregnancy or it could be a miscarriage. I would be at 3 to 4 weeks pregnant. I’m praying and hoping it’s just too soon. Does anyone know how many week you have to been until you can see your baby?