Ok. Thanks for the tips.
It´s an 300x480 image cause that is the size of my game background.
But, sorry for resubmit :_)
Surely you can redo that sky without the filters, right? It calls for some background. Anyway you probably used some soft tool here too, seeing the colors.
The pixelling is very rough. Honestly, this is way too large a canvas for a beginner ;)
The problem is this: pixel-art is about the precise control over each single pixel. In a 100x100 piece, there are 10000 of them; this is 300x480 = 144000. See?
Also you can edit a piece, no need to resubmit.
Some users told me that I can´t submit it with the sky cause is not pixel art :_
Oh, and it´s the same cave.
More tips: practice on small pieces before you invest enormous time in the whole game art; consider tiling.