I’m very scared 😩

I had my dating scan today and my app says I should be 8 weeks and one day according to my last period. There was a sac but no baby she even did an internal and still no baby. I went back to my doctor and did another blood test straight away. I got my results today and it said yes I’m pregnant just very early maybe 3-4 weeks. I have to do another blood test in the morning if the HCG levels go up it means a good pregnancy if not she said it’s not good. I’m very worried and have hope that everything will turn ok. Just wondering if this has happened to anyone else. Positive thoughts is all I have.