Your only hope by showing up is that the citing officer isn't there. If they don't show up you win by default. Although that doesn't happen too often now as the police are paid for their time in court.
Not only that, but officer court appearances are usually all scheduled on the same day. The officer won't just have to show up for one ticket, but five or six tickets. So he's not likely to miss.
I can tell you how it works in Virginia, but I can't really tell you California without more information. It's still technically a criminal charge, so one would think a court date is required. Look at the summons/citation and see if it lists a court date.
According to this website
, you can show up, have the charges read to you, and enter a plea in person. It sounds like you want to plead guilty but give an explanation so you can see if the Judge will let you do that. Alternatively, you could plead not guilty, let the officer present the evidence of guilt, testify on your behalf on your side of the story, and let the Judge convict you with the hope that he reduces the fine. You can also talk to the prosecutor before trial (explain that you are unrepresented by counsel) and see if they offer anything less than what the officer offers.
You also have an option of Trial by Written Declaration. That means you can argue your case in writing instead of orally. It doesn't sound like this would be beneficial to you.
All this being said, I'm not sensing any mitigation. It sounds like you did exactly what the statute prohibits. It sounds like the statute is designed to encourage a full stop before the railroad crossing unless traffic is light enough for you to move across it completely before you stop.