Can I want something bad to happen to me?
What bad thing do you want to happen to you?
I want to punish myself.
You should not want something bad to happen to you. It could be permanent and life changing for the worst.
I'm hoping I get a long jail sentence so I can focus on myself.
If you want to focus on yourself, then you should just put forth the effort. Going to jail will not help you as much as you think that it will, and it could ruin your life even further. The only person that can help you, is you.