Why does the part's texture keep glitching out?

I'm trying to make a cool background for my shop where a part looks like its moving but its actually the texture and size but still staying at the same position and kinda the same size. The Texture keeps glitching out once it reaches its maximum size which is 70 for the Y value. I've tried several times but nothing is working :/

The part is sized (94.56, 58, 2)

local Pos = script.Parent.CFrame
local MaxSizeY = 70
local SizeDelta = .1

while wait() do
    script.Parent.Size = script.Parent.Size+Vector3.new(0, SizeDelta, 0)
    script.Parent.CFrame = Pos*CFrame.new(0, -SizeDelta, 0)
    if script.Parent.Size.Y > MaxSizeY then
        script.Parent.Size = script.Parent.Size-Vector3.new(0, SizeDelta*1.2, 0)
        script.Parent.CFrame = Pos*CFrame.new(0, -SizeDelta*1.2, 0)
    end
end