Dats pretty nifty, i really like the shape of the landmass.
I can't say what might have happened to the brightness though, been awhile since i've gone through that method.
Have you tried turning off layers one by one to track down where it happened? Once you find the culprit, you could try applying some curves or adjusting the levels to brighten it up maybe.
Though Ascension might be a better guru to answer this one