I'm thinking you may want to learn more than one song in the 6 weeks. Reason: If they do pick you up, you will have to learn a lot of songs in a short period of time to be ready to hit the stage with them. If you have one song down and 2 or 3 more kind of worked out you will be in a better position to impress them and cut down what you have to learn before you're ready for the stage.
I would wish you luck, but if you are ready you will not need it. Go rock them.