What if I forgot to file a w-2 form

You should wait until the return is either accepted or rejected.  If your return is rejected, you will be able to add the W-2 before you resubmit.  

If your return is accepted, you can amend, or correct, your return if the original entries were incomplete. There is no additional charge to use Turbo Tax to amend your return, but you will need to mail in the amended forms, as the IRS does not accept e-files on amendments.   

Here is a Turbo Tax FAQ with step-by-step instructions for amending 2016.