I want to cut contact with my 13 year old sister.
What is your reason for wanting to cut contact with her?
She is a really boring and stupid kid.
It's up to you what level of relationship you want with your sibling, but it's a good idea to try to remain civil. Cutting all contact with your younger sibling will ruin your relationship with her, and make it harder to reconnect when you're adults. If you have a problem with your little sister, then try to work things out with her.
I can't. I want to hurt her because I want to be the only child.
You should not be so mean to your sister. She is part of the family so you really need to do a better job being understanding towards her. The hate you hold for her is only going to weigh you down in the end anyway.