If you made a Roth IRA contribution for 2017, you must enter it under Deductions & Credits -> Retirement and Investments -> Traditional and Roth IRA Contributions, not as prior-year contributions. However, if the Roth IRA contribution you made in 2017 was made between January 1 and April 18, 2017 for the 2016 tax year, then it needs to be entered as part of total of prior year contributions.
