So terrified!

I had a missed miscarriage of my first ever baby and pregnancy in August of this year. We were into our second trimester but not far enough along to be considered a stillbirth. Just a late miscarriage. I know logically that me having hashimotos thyroiditis could be the likely cause, but we are now 7 weeks and 6 days pregnant with our rainbow and I am TERRIFIED! I went to the ER last week cause I was cramping and scared. They gave me an antibiotic shot to prevent a possible UTI that they thought I was having and did an ultrasound. Baby was measuring a few days behind but my hcg levels were 92, 689. And baby's heartbeat was 128. So pretty good at this stage. I am four days away from my first ultrasound that I actually get to see (the hospital wouldn't let me see it when they did one on me). I just feel so impatient and terrified that when I go in the room for the ultrasound that baby won't have a heartbeat...any advice?