I Don't believe you've " messed this piece badly.. " Your image is done how you see it at whatever level your at, When I first came here I think how bad I was ( and still are, yes still are because I still have a tone to learn ). I made images where i tried to put too many objects in to the scene, Then when i got over that I had to learn how to blend them all with an overall colour balance, Lighting, depth, composition, Atmosphere, and still learning many other aspects of creating art.
So don't be put off, The comments are there to help to you, not slam you, And by the way, I was WAY WAY Worse then you when I started using Photoshop, so chin up and carry on.
OH, AND I ALSO MADE many many dark images as IamSam will tell you, so your not on your own.