Can I cancel a lease within 3 business days of signing it.

Some contracts provide for a "right of rescission" after 3 business days, but a real estate lease is not one of them.  In this instance a contract is a contract.  What you should do ASAP is to contact the landlord and see if they will just cancel it; you never know you might just get lucky, but more than likely they will charge some sort of cancellation fee.  Technically, if they do not let you cancel then you are liable for rent the entire term of the lease.  However, your landlord is under a duty to "mitigate" damages which means that they must use their best efforts to re-lease the premises.  Once they do you are no longer liable for any payments.

Again, contact the landlord sooner then later.