
Quoting
tbonez65
-What does this mean, a complaint?
It means that the DA has filed formal charges against you.

Quoting
tbonez65
-Is it wrong for the police officers to have said we weren't being charged, but now I am?
Actually, from your post, the police officers said that they were not going to charge you with a felony. They did not say they were not going to forward any charges at all. Rather than arrest you for a quite serious offense, it sounds like they forwarded a report to the DA for consideration of lesser charges. After such consideration, the DA decided to charge you and your friends with a lesser charge. That may sound like splitting hairs, but the officers actually gave you quite a break.
12303 Any person, firm, or corporation who, within this state, possesses any destructive device, other than fixed ammunition of a caliber greater than .60 caliber, except as provided by this chapter, is guilty of a public offense and upon conviction thereof shall be punished by imprisonment in the county jail for a term not to exceed one year, or in state prison, or by a fine not to exceed ten thousand dollars ($10,000) or by both such fine and imprisonment.
A molotov cocktail is a destructive device, defined here:
12301.(a) The term "destructive device," as used in this chapter, shall include any of the following weapons...
(5) Any breakable container which contains a flammable liquid with a flashpoint of 150 degrees Fahrenheit or less and has a wick or similar device capable of being ignited, other than a device which is commercially manufactured primarily for the purpose of illumination.

Quoting
tbonez65
-Is this a felony charge? What are the repercussions?
No, you are being charged with illegal burning, a misdemeanor.

Quoting
tbonez65
-Anything I should do?
It would be a good idea to consult a criminal defense attorney. It is likely (presuming you have a previously clean record) that an attorney can settle this for a fine and probably some probation time.