When I was younger, I was always a little "afraid" of girls in a way... but as I have gotten older that seems to have disappeared. The fact I am now married is irrelevant, because I snagged my wife about the time I was able to walk up to a girl, introduce myself, and grab a date... all within 30 seconds.
My advice is to just ask her, but be confidant when you do it. Next time you see her, avoid saying things like "um" and "uh" and just slap it down for her... "Hey, you know I was thinking... I really like you a lot and I'm pretty damn sure you like me a lot as well. I'd like to take it to the next level. How about [insert fun thing to do] tonight?"
Keep it short and sweet and to the point. Look her in the eyes and stand like a man when you do it. If she says "Yes" then try to avoid looking too excited in front of her (IE wetting yourself or something) and be all like "OK great then
That's probably about the best I can do based on my experience in life up to this point.
Good luck mate
~Sol
*PS*
If she seems unsure, or says anything along the lines of "I don't know if it will work out." Then do what I did and reply with "Sure it will... you know why? Becuase I'm the best there is and I won't let it NOT work out ." Then whisper in her ear "And I can prove it..."
You don't actually have to prove anything at all... unless of course by nature you are a total asshole that likes to beat women or something, then well... yeah lol.