As a native English speaker, I would say that it is/would be more polite to say: "Please leave the room. You are not allowed/permitted to stay in this room. "
I hope this helps you 😀
Unless you have specific authority, like a police officer, a school teacher or a judge, to order somebody to leave a place, it is probably better to avoid being rude/blunt by saying Get out!
An exceptional situation would be for the purpose of saving people's lives in an emergency when you don't have time to worry about upsetting people when you could shout Get out of here/there, there's a bomb in this /that building now!