Signs of a miscarriage?

Im 8 weeks pregnant and I woke up in the middle of the night to go to the bathroom and there was a bit of brown blood in my discharge when I wiped. Is this the start of a miscarriage? I didn’t have any more blood when I woke up this morning but just now I had a tiny bit more. I have my first ultrasound tomorrow, and I’m so afraid I’m going to go and they won’t be able to find the heartbeat.