If the question in WO-I about "Is this the final quantity" was no, and the WO was not closed, then just do a lookup in the date field in WO-I and select the WO with the extra labor and back that reciept out and then re-do it.
 
Everything will post nicely.
 
If the question was answered yes and the WO was closed then the extra cost WILL go to the WIP Variance account.  Nothing that can be done about that unfortunately.