I think a darker shade of each colour for an outline would still look cartoony but a tad better but thats just my opinion, it still looks fanastic, it's a great idea. Good luck, bet you've got a great chance of winning
I dunno, some people can spend forever on something without it being as good as that, whereas others can whack up fantastic pieces in minutes. I think it's all about natural talent. Which I can say I don't have :-P but I enjoy failing miserably anyway.