Many errors in this hat. I understand that you tried your best, but bear with me.
First step; fix outline.
Your outline is consisting with one thin and the other 2x thick. Have it thin. Keep it clean.
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Not yet, buddy boy.
I don't know how you shaded your brown, but it looks pillowshaded.
http://opengameart.org/content/chapter-5-color-palettes
Take a look at that.