How to make text move across screen?

How can I make this repeat the message after it is off the screen?

right = false

left = true

speed = 10000

while true do
    wait()
    if right then
        for i=1, speed do
            script.Parent.Position = UDim2.new(i / speed,0,0.5,0)
            wait()
        end
    end
    if left then
        for i=1, speed  do
            script.Parent.Position = UDim2.new((speed - i) / speed,0,0.5,0)
            wait()
        end
    end
end