Yes. You should amend your federal tax return. For any nondeductible Traditional IRA contributions that you have made or will make between January 1, 2017 and April 18, 2017 that you have designated as 2016 contributions, you would need to amend your federal tax return in order to report your nondeductible contributions on Form 8606.
Please refer to the following FAQ for instructions on how to amend your tax return. https://ttlc.intuit.com/replies/5567856
With respect to your state return, whether or not you should amend it will depend on the specific state . Please refer to the following FAQ and click on your state to access the appropriate website. https://ttlc.intuit.com/replies/4801660
