How To Lock My Field Of View?

So I Been Scripting For Few Weeks And I Want To Lock My Field Of View Heres My Script

local offset = Vector3.new(-5,50,0)
local fieldOfView = 90
local player = script.Parent.Parent
local camera = game.Workspace.CurrentCamera
local runService = game:GetService("RunService")

camera.FieldOfView = fieldOfView
local function onRenderStep()

 local playerPosition = player.Character.HumanoidRootPart.Position
 local cameraPosition = playerPosition + offset
 camera.CoordinateFrame = CFrame.new(cameraPosition, playerPosition)
end

runService:BindToRenderStep('Camera', Enum.RenderPriority.Camera.Value, onRenderStep)