I suspect that you did an In-plan Roth Rollover (IRR) from the traditional account in the 403(b) to the designated Roth account in the 403(b), not a rollover to a Roth IRA, or at least that's what you told TurboTax. Unfortunately, IRRs are not permitted to be subtracted from AGI the same way that rollovers from an employer plan to a Roth IRA are when determining the MAGI for the purpose of a Roth IRA contribution.
