It is common to omit reporting a Form W-2 on your tax return. You file before they arrive, they get lost in the mail, get lost in your house or get tossed along with junk mail.
Since the IRS requires you to report all your income, you should amend your return, but only after the original return has been completely processed (refund received or payment accepted). If you prepared your original return in TurboTax Deluxe, you should be able to amend it with Deluxe.
If you don't file an amended return to report the Form W-2, the IRS will send you an automated Notice of Proposed Increase in Taxes later this year.
They will calculate the tax due (plus interest and penalties) and you can send them a check (no amended return necessary).
