If this lowers your payment and is the only change, you should redo the contract.
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What I think you wrote is that instead of the interest being written as 2.9%, the rate written in your contract is now 0%. The dealer is now asking you to come back in to fix the error.
Did you and the people at the dealership discuss the interest rate being 0% before signing the agreements? If the agreed interest rate was 2.9% and the 0% was mistakenly written in, the dealer likely will have a good chance of asking a court to correct the error.
Moreover, your paperwork likely states that the loan has actually not been approved but that the dealership would try to find financing for you. Unless you have extremely good credit and there is a special promotion from the manufacturer going on, you likely will not get 0% financing. That is, the dealership will not be able to find a loan for you and you would need to return the car anyway.
You should review your specific facts with your attorney to find out your legal options.