licensing agreement without a previous contract

A Friend called me today, and said that he had a band in his studio shooting a music video, and the photographer they had hired to shoot behind the scenes did not show up, and asked if I could sub in for a quick easy 200$... I also managed to discuss a full shoot at a later date to be announced with this musician, Tonight however, I managed to take a photograph that was just incredible, Its by far album cover worthy, and this girl may actually have potential... Due to the rushed nature of this job, and truthfully the fact that I was not expecting to get anything of this caliber from Behind the scenes shots... I did not have a contract in place. She payed me Cash on the spot. 

What can I do now to make sure I'm protected, and retain rights to this photograph in the future.