It is unlikely that you can get this adjustment if you (or an employee or agent of yours) viewed the space prior to leasing it: in that event, a court would likely conclude that having seen the space and then leased it, you leased it based on the space as it actually was and was actually inspected by you--and not based on the square foot measurements. When you actually see what you lease before entering into the lease, courts are very reluctant to modify, change, or overturn the lease.