Accidentally listed my Simple IRA as a Roth IRA on my (accepted) 2018 federal tax return. I amended the error. No refund or amount due. Do I need to mail the amended copy

[AlexisH2]

Yes it's a good idea to still send off the amended return 

[dmertz]

Since the amendment results in no refund or balance due, the only place that your tax return might be affected is in the details of Form 8880 if this form was included in your originally filed tax return.  Otherwise there is actually nothing at all changing on your filed tax return and there is nothing that is being amended.  Unless you must submit a changed Form 8880 with your amendment, the IRS will likely reject the amendment if you send it since the Form 1040X will show that nothing changed.

[dmertz]

You'll still want to retain the corrected 2018 tax file for transfer into 2019 TurboTax so that 2019 TurboTax will have the correct amount for your basis in Roth IRA contributions.