Hi Moose
There won't usually be a cooling off period under a residential lease (which I am assuming yours is?) unless the actual lease document says so. I.e., there is no cooling off period implied by legislation.
Do you have a copy of the lease? I would look through this and look for details of a cooling off period. If there is none (which I suspect may be the case), then find the section that deals with termination of lease and states the ways in which the lease may be terminated. If, upon reading this section, you don't feel there are any avenues for you to terminate the lease easily then you may consider a more practical approach and talk to the agent direct to explain your situation.
The agent may want to charge you a re-letting/advertising fee or some other nominal fee for breaking the lease, but this can be negotiated between you and them.
Best of luck!