Anti-Zoom script which doesn't fill whole screen with GUI ?

So i've got this anti zoom script which doesnt let player zoom out within radius. And also whenever it does that it's guy doesnt fill the whole screen i tried adjusting gui's size heres how it looks: http://prntscr.com/86fj5l i've marked the area with yellow color.

Heres the local script

wait(0.1)
local maxZoom = 50
local cam = game.Workspace.CurrentCamera
local player = game.Players:GetPlayerFromCharacter(script.Parent)
local gui
while (not gui) do gui = script:findFirstChild("CamGui") wait() end
gui.Parent = player.PlayerGui

function loop()
    while ((player.Character) and (player.Character:findFirstChild("Head"))) do
        local dist = (cam.CoordinateFrame.p-player.Character.Head.Position).magnitude
        gui.Screen.Visible = (dist > maxZoom)
        wait(0.2)
    end
end

loop()