Think I found a calculation error in Form 4797

I'm trying to finish up my Rental Property sale in TT for Business and in the summary of Part III Gains on form 4797 sale of business property. On line 30 I have a total gain of $335,646. Line 31 is $0. Line 32 is also $0. The form states on line 32; subtract 31 from 30, so I would think that it should be $335,646. but as I said it shows $0 for the amount.  Any pros want to verify that I'm right or if not, why. TIA Bruce.