Have you made sure this isn't just a cock-up? Hanlon's razor suggests that you shouldn't attribute to malice that which can be adequately explained by incompetence.
Assuming that you have talked to the agent and they are insisting that the unit on the lease is the unit you rented. On the face of it, you signed a lease to rent unit B, the fact that you saw and were given information about unit A is irrelevant.
From a strict contract law position, the parol evidence rule, which is good law in Maryland, means that when a contract is reduced to writing then that is the entire agreement between the parties and you cannot turn to prior discussions or correspondence. The justification for this rule is that parties may adopt many positions during negotiations and that they may be modified or abandoned many times during those negotiations but when the final agreement is reduced to writing then it says what the parties mean it to say.
However, where there are allegations of fraud, accident or mistake, you can consider matters circumstantial to the execution of the contract.
I really think that you will have a hard time proving fraud and, to be honest, I don't know what Glass v Doctors Hospital, Inc. 213 Md. 44, 56 (1957) meant when they uised the term "accident".
What you have here is a unilateral mistake i.e. a mistake made by one party (you). Unfortunately:
It is the rule in general that a contract will not be reformed for a unilateral mistake, nor does such a mistake, of itself render the transaction voidable. However, equitable relief by way of rescission1 may be given if the mistake relates to a material feature of the contract, if it is of such grave consequence that enforcement of the contract as made will be unconscionable, if it occurred notwithstanding the exercise of ordinary diligence by the party making the mistake, and if the other party can be put in statu quo.
Of the four elements, you are good to go on 1, 2 & 4. No 3 is where the trouble is - "it occurred notwithstanding the exercise of ordinary diligence by the party making the mistake". Without knowing all the surrounding details (e.g. were you shown multiple dwellings, where addresses sent in correspondence etc.) I can't really comment on if you showed "ordinary dilligence" or not.
1 Rescission means the contract never happened - everyone goes back to the status quo. this remedy is not available where third-parties would suffer damage from this.