1) There is no penalty on your tax return for an excess contribution to a 401(k). The only requirement is that it appears as taxable income.
2) No changes to any Forms W-2 should be made.
3) If TurboTax does not automatically include the excess as income on your tax return, go to Miscellaneous Income, 1099-A, 1099-C -> Other income not already reported on a Form W-2 or Form 1099, answer Yes, continue forward and answer Yes when asked, "Did you earn any other wages?" Select Other, then enter the amount of the excess deferral with the description of "Excess salary deferral." TurboTax will include the excess on Form 1040 line 1.
