Just understand the basis of your fear. Are you afraid you won't withstand the rejection? Nah! You'll survive it! Are you afraid you'll be forever outcast amongst your friends? Nah! They get it! Are you just uncomfortable to put yourself out there? Yep! And, that's okay! You are showing courage, and you can be proud. :) Good luck! The right girl will say yes. You're young. Have fun!
Ok i think i can help you in this problem. Basic reason for you to be nervous and scared is that u are afraid she might say 'no' to you. So how u deal with it. U need to improve yourself. Improve meaning make yourself more attractive and appealing. The more good looking u are,the less afraid are you. And not only judge yourself on facial looks,even if u are not that much good lookin,but have sense of style and fashion,have a personality. HAVING A GOOD PERSONALITY IS THE MOST IMPORTANT THING,SO DONOT MISS THIS OUT