Your extension gives you until October 15, 2019 to file your 2018 tax return. After that date, e-filing will be closed permanently. Then a 2018 return has to be printed, signed and mailed. When you requested your extension you were supposed to pay your estimated 2018 tax due--the extension did not give you extra time to pay.
When you requested your extension you were supposed to pay your estimated tax due. Did you enter the payment you made into your tax return? Go to Federal>Deductions and Credits>Estimates and Other Taxes Paid>Other Income Taxes