You gotta do it. I know it takes stones.. I think any guy will vouch that the first time they asked a girl they liked out was absolutely brutal, but you're going to regret it somewhere if you don't. I hate to be a jerk, but if you're really only acquaintances with her, and not like "best friends" or something, you've got little to lose and everything to gain. Not doing anything sets a crappy precedent for the future.. at some point you're going to have to go up to a girl you like and are probably intimidated by and ask her out. If it works out, it's a dream, and if not, it'll hurt, but you've got something to build on for next time, and it only gets easier after the first.