Is a piece of paper that is typed, a valid lease?

When I moved into a town home, I signed a regular piece of 8 1/2 by 11 paper that stated I would rent a room until September 31, 2011; I paid May's rent, loss my job in Arizona and found another job out-of-state, can I leave without retribution? After signing the lease, I was informed that I needed to pay a parking fee for the H.O.A of the community the dwelling is in; since that was not stated in the piece of paper I signed, does that give me grounds to break the lease. The landlord (who is also a roommate) knew about the fee however, never mentioned prior to signing the paper. Is the paper I signed more or less a good faith agreement and not a lease?