Cancelling a Purchase Agreement

I entered into a purchase agreement with the seller's agent representing me as I did not come with an agent. I've sent a text and email to the agent that I would like to cancel the contract. Do I need to formally sign something sent from him and have the seller's sign as well? I am not planning on closing but wondering if there's any liability or timeframe by which I need to sign something official or if my messages to the realtor is enough. Please let me know thanks!