Despite all the risks, if your gf is a person who likes attention, or don't mind being the centre of attention, she might like your way of proposal. Its crucial to know what your gf wants. People will tell you: "no don't do this", but it's your proposal, and she is your gf. If you are sure she will like it, go on. But like other forummers said, find out whether your gf is really ready for marriage.