I am trying to create a formula in which adds as well as subtracts.

Ginna, can you choose a record that you feel is incorrect and tell us what value is in each of those 7 fields.  My guess is that you are mixing up your "signs", for example maybe you are subtracting a [commission holdback], but perhaps what was in that field was already a negative. 

Please give an example with the actual values in those 7 fields.