Should TT prompt you when it adds underpayment penalty for state? I only noticed when printing forms. There were no prompts for me to review & I actually shouldn't owe.

The review forms section is before the filing for exactly that reason, catching things that need correction. Great job! Simply go back into the state and go through that section to make the selections that exempt you.

If you filed already,  contact your state department about submitting the form or amending. Each state is unique in how things are handled. You may have an easy upload available. See How do I contact my state Department of Revenue?