Debounce and Elseif Statement Troubles?

I've been making a GUI Menu. All the code is inside a localscript. My problem is that in my elseif statement, instead of having to click the GUI just once, I have to click it twice. I would like it to only have to be clicked once. I have tried using a regular if else statement in the past as well, and I thought an elseif statement would help it. But the same result came. I am also unsure how to insert a debounce and if this is relevant to having to double-click the menu to close it. Here is the code:

local gui, button, buttonm1 = Instance.new("ScreenGui"), Instance.new("TextButton"), Instance.new("TextButton")
gui.Parent = script.Parent

button.Parent = gui
button.Position = UDim2.new(0, 3, 0, 3)
button.Size = UDim2.new(0, 200, 0, 75)
button.BackgroundColor3 = BrickColor.new(0, 0, 0).Color
button.AutoButtonColor = false
button.TextColor3 = BrickColor.White().Color
button.BorderColor3 = BrickColor.White().Color
button.BorderSizePixel = 3
button.Text = "Menu"
button.Font = Enum.Font.ArialBold
button.FontSize = Enum.FontSize.Size18

buttonm1.Parent = button
buttonm1.Position = UDim2.new(0, 6, 0, 6)
buttonm1.Size = UDim2.new(0, 388, 0, 63)
buttonm1.BackgroundColor3 = BrickColor.new(0, 0, 0).Color
buttonm1.TextColor3 = BrickColor.White().Color
buttonm1.BorderColor3 = BrickColor.White().Color
buttonm1.BorderSizePixel = 3
buttonm1.Text = "Run"
buttonm1.Font = Enum.Font.ArialBold
buttonm1.FontSize = Enum.FontSize.Size14
buttonm1.Visible = false
buttonm1.BackgroundTransparency = 1
buttonm1.TextTransparency = 1

button.MouseButton1Down:connect(function()
    if button.Size == UDim2.new(0, 200, 0, 75) then
        button:TweenSize(UDim2.new(0, 400, 0, 150))
        while button.TextTransparency < 1 do
            button.TextTransparency = button.TextTransparency + .05
            wait()
        end
        wait(.3)
        buttonm1.Visible = true
        while buttonm1.BackgroundTransparency <= 1 do
            buttonm1.BackgroundTransparency = buttonm1.BackgroundTransparency - .05
            buttonm1.TextTransparency = buttonm1.TextTransparency - .05
            wait()
        end
    elseif button.Size == UDim2.new(0, 400, 0, 150) then
        while buttonm1.BackgroundTransparency < 1 do
            buttonm1.BackgroundTransparency = buttonm1.BackgroundTransparency + .05
            buttonm1.TextTransparency = buttonm1.TextTransparency + .05
            wait()
        end
        buttonm1.Visible = false
        button:TweenSize(UDim2.new(0, 200, 0, 75))
        while button.TextTransparency > 0 do
            button.TextTransparency = button.TextTransparency - .05
            wait()
        end
    end
end)

Again, my essential problem is my pet peeve of having to click twice to close the menu. If there is any reason why it has to be clicked twice, I am unaware of it. I would also greatly appreciate an answer on if a debounce is necessary to execute the script more efficiently. Thanks!