Overhead Health Gui not working?

Hi, I have a Overhead health gui that allows people on the server to see the amount of health you have. I have a script named "OverheadGuiScript" which is a normal script in StarterCharacterScript and a billboard gui named 'HealthGui' in it as a child. Under the healthgui there is a frame called Background and a text label called 'Indicator'. Under Background is a frame called 'Health'. The problem is that the health bar is not going down and the indicator is not changing at all. Please help.

OverheadGuiScript:

local char = script.Parent
local humanoid = char:FindFirstChild('Humanoid')
local healthGui = script.HealthGui
healthGui.Parent = char.Head
	 
	humanoid.HealthChanged:Connect(function()
	    local healthColor = Color3.fromRGB(255,0,0):Lerp(Color3.fromRGB(85,255,0),humanoid.Health/humanoid.MaxHealth)
	local healthChange = humanoid.Health/humanoid.MaxHealth
	healthGui.Background.Health:TweenSize(UDim2.new(healthChange,0,1,0),"In","Linear",1)
	healthGui.Background.Health.BackgroundColor3 = healthColor
	healthGui.Background.Health.Indicator.Text = "Health: ".. math.floor(humanoid.Health).."/"..(humanoid.MaxHealth)
	end)