You have until October 15, 2019 to e-file your 2018 return. After that, e-filing will close permanently and you will have to print, sign and mail your return.
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
Also Online will close soon after Oct 15. So if you can't finish and file by then you will need to download the .tax2018 file before closing so you can finish in the Desktop program. If you are getting a refund there is no penalty for filing late. You have 3 years to to file for a refund.