Thank you for your question. I look forward to working with you to provide you the information you are seeking for educational purposes only.
Unfortunately, legally under NJ law, there is no legal "buyer's remorse" law for purchase of vehicles, whether you drove it off of the lot or not. The purchase of a used car in NJ is considered as is unless you get a written warranty to the contrary. The courts hold that a used car purchase the buyer is legally liable for inspecting the car before buying and the courts use the term, "caveat emptor" when dealing with the used car purchase (buyer beware).
Now, with the legal issues explained so you know that if you push them you legally do not have a stand under the law, in most of these cases it depends on your negotiation
skill as to whether or not they will let you out of the purchase. If you did not put any money down and did not sign any loan agreement, then if you do walk away the chances the dealer will sue for breach of contract are slim to none.
If you did pay or sign a loan agreement, then it is up to the dealer to let you out of the agreement, since people are bound by the contracts they sign and you would expect the contract to be enforced if you went in tomorrow and they suddenly wanted to charge you $1000 more than you agreed upon and they have the same right to bind you to the agreement you made. So you would have to negotiate with them to cancel the contract in this case and it is possible they could force you to complete the sale or make you forfeit your deposit. If you used your credit card, they could charge the deposit to the card and then you would have to file a dispute with the credit card company and many times they will not get involved claiming this is a civil matter of breach of contract.
Based on what you stated, these are the legal options you have.