Now that you have just about everything you need to get the girl, you want to keep her! One common mistake: being clingy and overprotective.
I'm not saying that you should act like you don't care. What I am saying is that when your girl doesn't return your call within five minutes, don't freak out. When she's hanging out with her friends and one of them happens to be a guy, don't freak out. When you're at the mall together and you catch a cashier staring at her, don't freak out.
Please don't be the boyfriend that is taking her away from her friends, or complaining that too many other guys are interested in her. You don't want to be the subject of gossip during late night sleepovers. (Yes, we do that.)
Everyone needs their space, and girls are no different. Protect her and care for her, but don't take away her freedom.