Some fortune-teller said that I was not a mortal in my previous life but something in the sky. Any previous lives? Do people in this life have to bear the mistakes of previous lives?

There are past lives and this life. If you enjoy your blessing in heaven, come to this world to continue your practice.

Or you are sent by heaven to help the poor, and you come with a task.

Anyway, remember that you are yourself now, and no one can replace you. You must practice hard, or you will fall into hell and suffer from reincarnation.