The short answer is, "pay off the balance."
The long answer is more complicated and may depend on the facts, such as where you reside and if the property is not your home, where it is, and your circumstances.
Finding a mortgage is a cumbersome process, and requires effort and expense to accomplish. It is the very opposite of an impulse purchase. The process can vary but it is regulated enough to disclose to the consumer the interest rate paid, points and other fees, the principal, and the net monthly payment, among other vital information. In addition to all of these things it is a legal contract that binds all signatories to its terms and conditions.
However, a mortgage is a contract and contracts can be broken under some circumstances. If there is fraud by one of the parties the law will not enforce the contract. If there is a mutual mistake in the expectations of the parties, the law will allow both to walk away. The law will not enforce contracts against anyone under the age of 18. The law will not enforce a contract containing illegal terms and conditions (a court would probably throw out a mortgage that contained a 200% APR.) Similarly, the law will either throw out or modify a contract that contains misleading or deceptive language, or a contract where one party coerced the other into signing. The law will not enforce a contract when the purpose of the contract is frustrated (a builder agrees to erect a house on land that washes away in a landslide before construction begins). Finally, the law may not enforce a contract where one party had no intent, at the time of signing, to live up to the contract (these cases are usually where one party thought the other was in on the joke).
The facts are significant in all of these cases where a court modifies a contract or tosses it out completely. You don't explain the reasons why you don't want the mortgage after one month, so it is impossible to tell what legal tools, if any, are at your disposal.
If any of the scenarios I mentioned above seem familiar to your situation, contact an attorney in your state who specializes in contract or property law. Otherwise, sell the property and pay-off the mortgage.
Remember, the last thing you want to allow is a foreclosure. Obviously, you had good enough credit to get a mortgage, so it would be unwise to allow a foreclosure, which at this stage would be easy for you to prevent, to destroy your credit score. Address this issue immediately.
I hope this information helps you Find. Learn. Save.