TurboTax has no way of knowing that you paid the tax. All it sees is the amount due on your tax return. If you already paid, and TurboTax is asking how you want to pay, say that you will mail a check. Then you will be able to proceed to file your tax return. TurboTax doesn't know whether you actually mail a check or pay another way, and it doesn't matter how you pay. By saying you will mail a check you are just telling TurboTax that you will take care of paying the tax due.
