Your extension did not give you extra time to pay your tax due. An extension only gives you extra time to get your documents prepared. You were supposed to pay your estimated 2018 tax due by April 15, 2019, so your payment is now late and is subject to interest/penalties.
https://ttlc.intuit.com/questions/2879424-how-do-i-print-my-4868-extension-form-after-e-filing-it-th...
https://ttlc.intuit.com/questions/2550071-does-an-extension-give-me-more-time-to-pay-my-taxes
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
When you prepare your 2018 tax return the amount on line 22 of your Form 1040 will show you the tax due.
**Disclaimer: Every effort has been made to offer the most correct information possible. The poster disclaims any legal responsibility for the accuracy of the information that is contained in this post.**
