How can I tell a girl with whom I have had a playful flirtation that I can't ask her on a date because I feel she is above my league?

I want to say it in a way that doesn't sound patronizing for it is the honest truth. If she were to date me I think she would be unhappy.

How can I tell a girl with whom I have had a playful flirtation that I can't ask her on a date because I feel she is above my league?
Post Opinion