Your webinar is fast approaching the 100 user limit and you will need to block any incoming users into your room:
As the host you can block access in two simple steps:
Step 1: Block Incoming Attendees
From the Meeting menu choose Meeting Access & Entry submenu. Choose teh Block Incoming Attendees command.
Step 2: Edit Blocked Message
As you choose this command, you will get a chance to edit the message that would be attendees would see when they try to access the room. If you are recording the event you can give instructions on how to request or access the recording after the session is over, or lead them to a link of where to register for future sessions.