If you requested an extension by April 15, 2019 then you have until October 15, 2019 to file your 2018 return. You were supposed to pay your estimated tax due by April 15, 2019. The extension gives you more time to get your documents in order--not 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
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