Even if it sounds like yes, it probably still means no. If you respect the girl, respect what she says and if not, do it anyway. It's just not worth it. It may only be an opinion, but my opinion is that you should follow the law on this one.
Try to get to know her better and then ask her out again at some later date. Don't take the rejection too personally.
Move on and find someone else, plenty more fish in the sea.
Get a cheeseburger anyway.