Alright. First of all, if you're sharing your magic then please share your full performance.
Second, look through the AudioSwap feature at YouTube. You may be able to legally use the song you want, so long as YouTube gets to put up links to buy the song. This varies by song/artist/record label, but give it a look. There should be something available, legally and ethically, that you can use.
Finally, there's no reason to tie yourself to widely-published music. There are a lot of pitfalls if you ever plan to go bigger than YouTube.