I joined some kids bullying another kid on the school bus
That is not nice. Why did you decide to be part of this?
If I don't feel good about myself, neither can anyone else.
You will not feel better by making others feel bad. That will create a cycle of everyone feeling bad.
Fuck that, people should feel bad when someone makes them feel bad.
What if someone were to bully you instead? I doubt that you would like that or think it will make you feel better.