Whoa, where do you see in all that that the visa you're applying for is only for 3 months?

There are a couple of things about 3 months past the validity of the visa (like for how long your US passport has to be valid) and a few other references to "3 mois" - but you're applying here for a long stay visa, based on your marriage to a French national.

In any event, as I understand the way the rules are now (per the Service-public website), you can go get married in France, but then you have to return to your home country (or where you were legally resident before your marriage) and apply for a long-stay visa as the spouse of a French national.

To get the list of stuff you'll need in order to get married in France, you have to go to the local mairie where your bf lives. There's a whole bunch of other stuff you'll need, and the specific items vary a bit from town to town.
Cheers,
Bev