Why isn't text appearing in the textLabel?

The script runs as soon as you hit play, meaning that the script will stop because the Frame isn't visible at the time it ran (which is as soon as you play/run the game, scripts run very fast). You can use the Changed event to check if the frame becomes visible.

function Changed()
if script.Parent.Frame.Visible == true then

    local textLabel = script.Parent.Frame.TextLabel_Roundify_12px.TextLabel

    local function typewrite(object,text)
    for i = 1, #text, 1 do
        object.Text = string.sub(text,1,i)
        wait(0.1)
    end
    end


    wait(.1)
    print("yes")
    typewrite(textLabel, "I have to get out of here...")
end
end

script.Parent.Frame.Changed:Connect(Changed)

Hope this helps. Also, I believe the line with textLabel would cause an error.