Your Official Marriage Certificate from India will is sufficient proof of marriage to USCIS.
If the Marriage document is not in English, you will need to have it certified translation into English and send to Immigration Service with the Original Certificate and Translation attached.
You do not need an "Affidavit of Marriage" from a U.S. lawyer.
Nikiki T. Bogle, Esq.
BOS LEGAL, LLC
Ten Post Office Square
Boston, MA 02109
Phone: (800) 342-1733 ext. 101