How to set the CFrame of a part continuously so that when it grows, it only grows in one direction?

I know the title of this is a mouth full, let me explain.

I have a script that clones the Player's LeftHand, and makes the real LeftHand invisible. After that, it makes the cloned LeftHand grow. But as you can see in the gif (here) It grows above and past the player's arm. I'm not really sure how to fix this, although I had a few ideas that failed.

Here is the code that I used:

script.Parent.NormalLeft.OnServerEvent:Connect(function(Player, pos)
	local LeftHand = Player.Character.LeftHand
	LeftHand.Transparency = 1
	local Stretch = LeftHand:Clone()
	Stretch.CanCollide = false
	Stretch.Anchored = true
	Stretch.Name = "GumFist"
	
	for i = 1,50 do
		Stretch.Transparency = 0
		Stretch.Parent = Player.Character
		Stretch.Size = Stretch.Size + Vector3.new(0,0.5,0)
		Stretch.CFrame = LeftHand.CFrame*CFrame.new(0,-4,0)
		wait(0.00005)
	end

end)

Thanks for reading

use Resize() instead. Here's an example with your script:

script.Parent.NormalLeft.OnServerEvent:Connect(function(Player, pos)
    local LeftHand = Player.Character.LeftHand
    LeftHand.Transparency = 1
    local Stretch = LeftHand:Clone()
    Stretch.CanCollide = false
    Stretch.Anchored = true
    Stretch.Name = "GumFist"

    for i = 1,50 do
        Stretch.Transparency = 0
        Stretch.Parent = Player.Character
        Stretch:Resize(Enum.NormalId.Bottom, 0.5)
        Stretch.CFrame = LeftHand.CFrame*CFrame.new(0,-4,0)
        wait(0.00005)
    end

end)