of course you have to amend. your current reported basis in IRAs is incorrect.
you attached 8606 to your original return, as required. Use form 1040x to correct information on an already filed return
Overstatement Penalty (from form 8606 instructions)
If you overstate your nondeductible contributions, you must pay a $100 penalty, unless you can show reasonable cause.
so I would file an amended return can't guarantee the IRS won't asses penalty anyway but you have nothing to loose. this will also result in the correct basis when you rollover 2018 tt to 2019. tt
You must have a copy of the original tax return you want to update.
The simplest way is to prepare your correct tax return (using TurboTax for example, or other means) and print it.
Then lay the paper printouts of both returns (correct and original) side-by-side.
You now have all the information needed to prepare Form1040X by hand.
It's pretty straight-forward.
The blank form in fillable PDF format and its instructions are available at www.irs.gov.
Mail to the same address you would mail your original tax
return.
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In this scenario, only Form 8606 is new or changed, and all of column B in 1040X should be zero, since you didn't take the deduction.
In Part III Explanation state
"here comes a changed Form 8606 since I never made the contribution".