No, it isn't. the "Self defence" excuse is when you have no other choice. In this case you did. you could have walked away, left the building. nobody was threatening you. In fact, you threatened them. You were looking for trouble, and you'd be facing life in prison if you'd have found it.
Not in my state. Retreat is not a prerequisite to use of deadly force. Furthermore, use of deadly force is allowed by any citizen to prevent a crime.