I want to return a lease car I got today?

I had a 2014 Honda CRV and it had a problem with brakes as it kept squeaking. I took it to the service center and they couldn't find any problem. So I talked to the sales guy and he t old me he can replace my car with 2015 Honda CRV. My remaining lease for 2014 model was 18 months. What I "thought" he told me was I can return my 2015 model in 18 months if it's in excellent condition. So I signed the contract. After doing so, I realized The lease was for 36 months. The problem is that I won't need the car that long and I want to cancel the contract. But he keeps saying that I cannot cancel the contract because I have already signed. I told him that I misunderstood the contract period but he was there was nothing he could do to help me. So I drive the 2015 model to my house. Is there any way to get my old car back?

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