My teacher found out I made a mean video about her?

As a teacher, I can understand the both of you. People your age are still unaware of reality. You're immature because you are still testing people and playing with their feelings to learn from the experience. You can tell her that you've thought about what you did and that you felt pressured. You should try your best to grow up and avoid doing things for the fun of seeing the end result. This could affect your whole life, so take it easy on yourself. You could forgive yourself by seeking peace within yourself and without the need of her forgiveness. That's a major lesson in the real world: we don't always get the forgiveness so we must find peace with what we can. One day, when you're all grown and working in something decent, come back to visit her and ask her forgiveness again. Good luck, child!