My game had a locked First person, but with the new roblox update, it broke the script. I found this in the wiki, but only works if you go in-game and zoom in your self.
local plr = game.Players.LocalPlayer plr.CameraMode = Enum.CameraMode.LockFirstPerson
You don't need a script for that, go to StarterPlayer then CameraMode then select LockFirstPerson.