Did you pay $100 with an extension to file? If your extension payment from 4868 line 7 did not automatically show up on 1040 line 31 you need to enter it. So make sure it's not already there before you enter it!
To enter the amount you paid with an extension (including state extension) go to
Federal Taxes (or Personal for desktop H&B version)
Deductions and Credits
Then scroll way down to Estimates and Other Taxes Paid
Other Income Taxes - Click the Start or Update button
Next page second section Payments with Extension
Either Visit All or Click Start or Update by the extension you paid
