Help?

just be yourself. doing that makes him know that he's meeting a normal girl, not another pop star or something which maybe makes him feel more comfortable. if you act like someone else while meeting him, maybe next time when you meet up with him again, you will have to act again, which is totally uncomfortable. so, why suffer the uneasiness when you can enjoy an awesome time with Justin Bieber?

First of all, congratulations! As far as your behavior goes, I'd try and tone down the extremes (the yelling and what I would call excessive smiling and laughing). And on the other hand, I think Justin's getting used to girls he perceives as excentric. So I'd try not to be overly concerned with embarrassing yourself.