Three bad guys against one hostage do not work in you favor. You are dealing with known gang bangers who care nothing about collateral damage. I'd be willing to bet that they would not pick a hostage that could probably fight back so your chances of being taken hostage go way down. With three armed robbers, the force is pretty overwhelming. I'm not sure if there was any body armor involved, but don't forget about the incident that the movie Heat was based on. Firing on someone with body armor would most likely be suicide.
Now say the perfect storm hits and you are taken as a hostage, and you happen to be armed (not too likely in California), and the bad guys do not discover your gun
, then the only opportunity to change the odds would be if the bad guys get distracted long enough as they are shooting at the police. I would seriously consider making a move since the police are already firing upon the vehicle. If I was being used as a human shield, my greatest chances for survival would be to act rather than being shot by the bad guys, cops, or both. I am not pretending to be Rambo or anything, but what else can you do?