Enter the amounts shown in box 12 of your W-2 exactly as they are, only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax. Do not enter them as IRA contributions, a 403(b) is not an IRA.
Although I think it's unlikely, if TurboTax warns you during entry of the W-2 that you are over the contribution limit, ignore the indication. If TurboTax will not allow e-filing with this condition present in your tax return, file by mail.
