Now that I've submitted and transmitted my return, does that mean I have paid the IRS?

Not unless you included your tax payment when you filed.   If you are getting a refund, you don't need to do anything.  But if you owe, you need to pay make a payment on the IRS site if you did not include the payment when you filed.

did you use the option in TT specifying direct debit? it's on the info page where you would ask for direct deposit if you had a refund coming. 

 I do, in fact, owe the IRS 2019 taxes. How can I review my filing to verify that I included my payment with Turbo Tax?