Intent to marry is one of the very few requirements for the K-1. An RFE wouldn't be the end of the world, and it is an easy fix.
However, here is something else you could try: you could send an amendment to your packet directly to the California Service Center. I did this for a document (final decree of dissolution), and it was accepted and we got no RFEs. Just write a brief, succinct cover letter and be sure to include the I-797 receipt notice number for reference. I would just write something like "we inadvertently omitted our statements of intent to marry and hope that it can be included with our petition."
Good luck.