Typically, there is a three day attorney review period where "legally" the attorney can reject the contract for any reason. I do not believe they have to disclose the reason, but if they know they can get a better price (whether actually receiving an offer or just from other data, such as appraisals or another comparable home that just sold), they can argue the attorney is advising them that they are getting short changed on this business transaction.
However, that said, the others are right. Consult your attorney, whom you've already paid. He/She will be able to read the entire contract for any contingencies for a way to keep the seller in the deal. I warn however, the boilerplate contract used in the State of NJ does not have anything I know of that would protect your interests in this case. It would've had to been a contingency/clause added to the contract by your agent/attorney.
Techincally, you made an "offer to purchase" that was accepted by the seller. That is a contract. It then goes through attorney review and upon both attorneys accepting the terms, it becomes a completed contract. During this Attorney review period, the contract terms can still be negotiated by both parties. There is a procedural part where the attorney "cancels" the offer to purchase contract then after all negotiations are done (or at the end of the three day period), they declare the contract valid in its final form.
The reason the contract isn't binding until the attorney reviews it (or the buyer/seller knowingly refuses attorney review) is because Real Estate Agents are not allowed to practice law, which includes writing up contracts. That is why there is a boilerplate contract for NJ (and most states) that was part of a big court case settlement between Lawyers and Real Estate Agents. Agents were allowed to use that contract drafted by the Bar Association, but had to disclose to their customers that they can have an attorney review the contract on their behalf. If they don't disclose that fact, there are legal ramifications against that agent/brokerage. It is up to the customer to seek an attorney in a timely manner and have the attorney response within that 3 day period.
I wish you luck in getting this deal completed if this is your dream home! At the very least, I hope you recover your expenses such as the legal fees from the seller. Let us know how this ends.
P.S. After typing all of this, I realized other people may flag me as I am not an attorney (I am a Realtor specializing in Bergen County), so I searched for a little bit on Google and found the following article by a NJ attorney regarding real estate contracts. It is essentially what I just said above. I hope this helps!