"Duress" is defined with a far greater burden than you have proposed and it extremely doubtful you will be able to avoid the contract with that defense. Had you signed it before you moved in, you might have had a better case.
There may well be a clause in the contract that says you have inspected the premises and accept them in their current condition. If so, that again will make it difficult for you.
Having said that, Missouri's defense under a case called "King v Moorehead" may help you - showing that the place is uninhabitable. To take advantage of that ,you have to pay the rent into court pending the outcome.
The bottom line is that no attorney can give you a complete picture without seeing what you signed and you need to see an attorney about that right away before you next pay any rent.
This comment does not create an attorney-client relationship. The law and its application by the courts is constantly evolving and changing. This discussion is not to be taken as a definitive guide, and should not be relied upon to determine all fact situations. Each set of facts must be examined separately with the current case and statutory law analyzed and applied accordingly.