Deductions & credits

Yes you need to amend the return if the return filed is incorrect.

As for the accuracy guarantee ... if you wind up owing after the correction due to this issue you can complete an accuracy guarantee submission :

Any calculation errors on the part of TurboTax are covered under the Accurate Calculation Guarantee. TurboTax will pay any penalties and/or interest due to a calculation error but not any taxes owed. The Guarantee does not cover any user entry errors or omissions.

See this TurboTax support FAQ for the 100% Accurate Calculation Guarantee - https://ttlc.intuit.com/questions/2566201-what-is-the-turbotax-100-accurate-calculation-guarantee

See this TurboTax support FAQ for submitting a claim - https://ttlc.intuit.com/questions/1901269-how-do-i-submit-a-claim-under-the-turbotax-100-accurate-ca...

See this TurboTax support FAQ for documents needed to submit a claim - https://ttlc.intuit.com/questions/1901060-what-documents-do-i-need-to-submit-a-claim-under-the-turbo...