Prevent re-joining an ended session

If you have the Named Host licensing, once you close the room and are not in it, users attempting to rejoin the room should either get a message that the Host has not yet joined and to please wait or they may get in the room if the session is still active but will be removed from the room if a Host is not present within 5 minutes. If you don't want the second option to be a possibility, you can turn on the Block Incoming Attendees option in the Meeting > Manage Access and Entry menu. You can have a customized message and this feature essentially locks the door to your room. You can enable this option before or after you use the End Meeting function. Since you are predefined with Host rights to the room, this option won't prevent you from getting into the room.

If you have Concurrent User licensing, you'll need to use the Block incoming Attendees option to prevent people from entering the room.