The amounts in box 12 with the codes of M and N appear on Schedule 2 (1040) line 8c with the notation of UT (Uncollected Taxes).
Therefore, if you are liable for these taxes (and it sounds like you know you are), then they must be entered when you enter your W-2 so that your tax return is correct.
I would encourage you to get a corrected W-2, so that what TurboTax sends to the IRS with your return matches what the IRS already received from your employer.
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