What do I do about what I did?

I did something horrible years ago. I threatened to kill someone and she was so scared she started crying. I did it out of a sick sense of happiness and love for others fear. I terribly regret and remorse what I did. I don’t know what I should do. I’m so scared. Some people have told me I should just commit suicide, and others say to just face what I did. I don’t know who this person is, but I want to at least apologize to her and let her know I will never hurt her again. I fear she will see me one day on the streets and beat me senseless or kill me for what I did. What do I do?