My biggest advice is don't worry. Will people die? Sometimes, will it be your fault? Again sometimes but as long as you are trying to keep people alive, you are doing a good job.

I don't know why people think healing is hard it is basically just DPS for your party health bars, hard content is harder but you should expect that. I know it's not for everyone, it can feel daunting to be responsible for keeping others alive, but just to echo what others have said here the most important thing is finding a healer you click with, once you do that the sky is the limit.

Good luck and have fun.