It is always best to have all of your information on your tax return, even if there is no apparent tax consequence. However, a non taxable pension may affect your taxability on Social Security.
If you do not file an amendment you may get a tax notice describing the effects of any change. This may take 6-9 months.
You could then review the change and make any adjustments necessary.
Please understand that a tax notice does not put you on a black list. This is a technical situation that happens frequently. It is not a criminal offense.
Or, you can prepare an amended return and see if there is any change before you mail it.