After you file

You should report in TurboTax the actual gain, which seems to be $345 in this instance. The Form 1099-B should list at a minimum the sale proceeds and either a cost basis of a positive amount or $0. If the stated cost basis is wrong, you should adjust it by entering the correct cost basis. You will see an option for doing this after you enter your Form 1099-B in TurboTax. That is all you need to do even if the Form 1099-B does not show a gain or loss amount.