Your accounts in the federal TSP are not IRAs. Go back and remove the entries you made for these contributions under Deduction & Credits.
Enter amounts shown in box 12 of your W-2 only in box 12 of TurboTax's W-2 form, nowhere else in TurboTax.
TSP is not an IRA or a Roth IRA. Qualified workplace retirement programs are governed by completely different sections of the tax law then IRAs and follow completely different rules. Even though they have a similar purpose. When TurboTax asks if you made contributions to an IRA or a Roth IRA, only report contributions that you sent out of your own money to a private bank or brokerage where you had established an IRA. Do not include money that was deducted by payroll deduction and placed in a workplace plan.
if you did not make contributions to a real IRA, then go back in TurboTax and change your answers. If you did make a contribution to a private IRA and it is considered excess because it is more than you were eligible for, you must remove the excess contribution before April 15 or pay a 6% penalty tax.