Why is my drawing script not working the way I expected it to work?

Alright, so I added a GUI and a frame under the GUI and a script under the frame. My script was this:

local player = game.Players.LocalPlayer
local mouse = player:GetMouse()
local frame = script.Parent
local x
local y

local pressed = false

mouse.Button1Down:Connect(function()
    pressed = true
end)

mouse.Button1Up:Connect(function()
    pressed = false
end)

while wait(0.01) do
    x = mouse.X
    y = mouse.Y
    if pressed == true then
        local dot = Instance.new("ImageLabel")
        dot.Parent = frame
        dot.Name = "Dot"
        dot.BackgroundTransparency = 1
        dot.Image = "http://www.roblox.com/asset/?id=3195888012"
        dot.ImageColor3 = Color3.new(0,0,0)
        dot.Size = UDim2.new(0, 3, 0, 3)
        dot.Position = UDim2.new(0, x, 0, y)
    end
end

I believe that the dot.Position is written out wrong. Anyone out there that knows how to fix it? Try it out yourself.