Is it wrong that I don't want to apologize for getting my friend grounded?
It could be, why won't you say sorry to them?
They don't deserve it. They stole something from my parents.
If they stole something and you told on them, you do not need to apologize because you were doing the right thing.  Your friend needs to be punished for what they did.
They deserve it and I don't feel bad about it.
You should talk to your friend and explain why you did not apologize for telling on them, and you should tell them they shouldn't steal from people.  Your friend will only learn if they are held accountable for their actions.