I’m guessing you mean the it only scales to the topbar and then the topbar shows the skybox. If this is the case then make sure you have ScreenGui.IgnoreGuiInset set to true. This will make the gui take up the entire screen (assuming you are using scale like @regexman mentioned).
“IgnoreGuiInset is a boolean property of ScreenGuis that, when set to true, will force the GUI Inset imposed by Roblox’s CoreGuis to be ignored by this ScreenGui and its descendants. This means that an element with a UDim2 size of {1,0},{1,0} will fill up the entire screen, without a 36 pixel gap reserved for Roblox’s top bar.”