Inventory Count help

We booked an Inventory for one of our Cost Centers last week and noticed this week that we accidentally marked one of our items with the wrong case count.  Is there a way to correct this?  I don't see an option to re-open or delete the count now that it's booked.  It won't let us enter a negative quantity in this week's Inventory that is currently open either.

For example, we received a case of tuna.  On our inventory (and in Manage Store) we have a primary unit for the case, but we also have a secondary unit as an Each.  We were supposed to put that we have (3) each, but instead put (3) cases.  Because the error was made on a booked Inventory, how do we correct this?  Do we have to enter the cases as Waste to balance out the count?