Has this happened to anyone?

I went to my first appt yesterday, I had an ultrasound done and the doctor only seen the gestational sac. He was saying I was showing about 5 weeks. He said I could of ovulated later and that could be why. He sent my to get my hcg level checked. He also said it could be how my cervix is laying too so maybe he can’t see anything yet. If you go by my last period I should be almost 8 weeks. I got my first positive pregnancy test on Sept 3rd. I have lots of symptoms. No bleeding or cramping which the doctor said to look out for just in case if it is a miscarriage. Please someone if you have had this happen, give me some advice or something because I am just distraught and I don’t know if I can handle having a miscarriage. I know it happens but I am just upset and these hormones are getting the best of me.