How to teleport to a private server in a place? (Like Tower Defense Simulator's teleport system)

I have a question to ask, I'm working a Tower Defense game on Roblox, and I've made a simple teleport script (as shown below). It's a place not a game that you teleport to. When you teleport it works but a player can join while mid-game, which I don't want. I want it like or similar to the teleportation system in Tower Defense Simulator and other games that use a similar way/style. I would love it if someone helped me! <3

~ notreallysupernova

local MapCollection = 5770100191
local MapID = MapCollection

function onTouched(hit)
      local player = game.Players:GetPlayerFromCharacter(hit.Parent)
      game:GetService("TeleportService"):Teleport(MapID, player)
  end


script.Parent.Touched:connect(onTouched)

print("Teleported to ".. MapID)