As the others advise, check with a lawyer. I'm not a lawyer, so this isn't legal advice. But based on my experiences in other areas, you might or might not have a binding contract. (For instance, although no money has changed hands, you have received "consideration"--a lease that does have value and a promise to pay.)
So there are all sorts of questions involved: Is actual payment required? Under what conditions may you cancel the lease? Are there contingencies in the lease that you could invoke? What sort of landlord-tenant regulations might protect your would-be tenant (or, possibly, you)?
Check with a lawyer.