wow you guys are cliche...

how old are you? she likes you right? she's your "girlfriend" right now correct?

Do something fun, then retaurant. like go to an amusement park... you'll have fun, talk, mess arround, laught and it wont be in such a formal place. After that you go to a restaurant.
Maybe a dancing class? just tell her that you need a partner for this class cause you have a wedding coming up.