How to make a session unjoinable from find session node?

i have a multiplayer fps game which i dont want to allow to give access to players after there are 100 players in the game disrupt it. i want to make a lobby were players can join until 100 players are there. is it possible to do this all just in blueprint.if you know please paste the pics of the code and explain it breifly as i am new to networking in unreal.
thanks in advance.