Having an extension for a 2017 return is meaningless at this point.  You had until October of 2018 to file that return with your extension.  So now it is just late.  If you owe tax due, you will be billed by the IRS for the penalties and interest that have been accruing.  TurboTax will not calculate that.  If you are getting a refund, there is no penalty for filing it past the deadline.

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

To finish a prior year return started in TT online:https://ttlc.intuit.com/questions/2559403-how-do-i-finish-a-prior-year-return-that-i-started-in-turb

When you mail a tax return, you need to attach any documents showing tax withheld, such as your W-2’s or any 1099’s.  Use a mailing service that will track it, such as UPS or certified mail so you will know the IRS and/or your state received the return.

Thanks for your quick response. I had filed my extension in April 2018 through Turbo Tax. I am looking for the submitted Form 4868 that I need. I assume that Turbo tax has a record of this. Where can I find it?