I remembered that I input my bank account info and chose the direct debit option while submitting my tax report via Turbo Tax. I always have more than enough money in that account waiting for it to be taken by IRS, but it never happened.
There must be something wrong with this dumb App. For a good user experience, if I did accidentally choose to mail the check myself, it should let me know clearly either on the UI or send me an email. The penalties plus the interest amount plus the Turbo Tax license fee is good enough to hire a tax accountant.
Sounds like you are unsure of how you chose to pay your tax due---you say "if I did accidentally choose to mail the check...."
Look at the electronic filing instructions that print out with your tax return, What does it say about how you will pay?