The TurboTax INCOME TAX program doesn't handle or cover GIFT TAX forms in anyway so it is not part of the interview and neither are the forms. The fact that this is not covered in the TT program is not really a reason you failed to file the proper gift tax forms.
The form 3520 is not gift tax it's an informational filing you file along (usually) with the 1040. Generally TurboTax will ask questions and indicate you may be required to file xyz form but we don't have that form. I knows it's still taxpayers responsibility