meaning should I add the amount I contributed to FERs and TSP as part of my IRA deduction?
No. The federal FERS and TSP are not IRAs.
Enter amounts shown in box 12 of your W-2 only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax.
FERS is your government Annuity. FERS payments should be handled as Annuity payments.