threatened miscarriage

Hi, I am 6 weeks pregnant. I went to the hospital today because I had some brown discharge. They said there was a tear around the yolk sac, which caused the bleeding. I had a scan and there was a heart beat....but I was told there is a threat of miscarriage. Has anyone else had anything like this? What do I need to do to keep the baby healthy? I'm very scared the tear will get worse. Does anyone know what causes these and how to avoid it getting worse? Any advice will be welcomed. Thank you!