I think you need to practice anatomy and posture.
One thing though, you know how you said "Screw you, it's perfect" to that guy?
OH MY GOD, don't do that man!
You need to take criticism, or you won't get anywhere man! You need to take what people say in account. That's the only way you'll ever be a good artist.
Otherwise, you'll end up making horrible art like this guy:
You're only 11 and I understand that but please, don't go insulting people that give you constructive crticism! You have potential man!!!