I'm not sure if you mean a Roth 403(b) or a Roth 401(k), but either way the account is not a Roth IRA. Enter amounts shown in box 12 of your W-2 only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax. In particular, nothing about this is to be entered under Deductions & Credits. Remove the Roth IRA contribution that you entered.
