I need your help...

[jettblack0110.livejournal.com]

So for a friend's birthday, I said I'd draw her a picture of dear Nick and Greg.  So I'm nearly done, but Nick just doesn't look right to me.  I think it's his mouth, but I don't know what to do.  It's pretty sad.  So if you could take a look and let me know...I could really use a moment of inspiration!  Thanks!

Here's the picture I drew....

Don't worry, I rounded out Greg's chin so it's not so square, and Nick is supposed to be biting his lower lip.  I just can't seem to get it right.

Here's the picture I'm referencing...


Any help you can give...thanks!