The default skin is specifically designed with excess background for these situations. The CD skins, on the other hand, don't fare as well on widescreen.
There is a widescreen-specific CD skin (cd6-1-ws.skn) that may work better for you. You may also want to try setting the FixedDimensio n setting in jukebox.ini; if your top and bottom are cut off, setting FixedDimension=Height will letterbox the skin.
--Chris