I checked my records and the IRS was right. I apparently filed with a non-final TurboTax file and had I used the right one it would have matched what the IRS said I owed. (I have multiple versions while working on joint of separate returns - TurboTax doesn't seem to have a feature to merge individual ones).
So I sent in payment and form before the new deadline.
A month or so I later after my payment I got a notice that I still owed the money and when I tried to call I never got to speak to anyone; this notice said I could file a petition to the Tax Court ($60 fee). Meanwhile I got a notice from the IRS that my account was settled. I included a copy of the cancelled check for the payment and that notice on my TaxCourt petition.
A few weeks later I got a notice about logging into the TaxCourt System to see the status; it wasn't very clear but said that something I submitted wasn't legitimate evidence?, but indicated that I'd hear something more soon (could her a court date?).
A few weeks later I got another notice and a phone call from someone in the TaxCourt who said I had to mail in a form with a signature indicating that I'd read the latest notice. I mailed that in.
Several days I got an email notice to login to my account and from there I printed the document signed by a Judge that said everything was settled.