It sounds lke you missed the second step in getting your fix-it ticket resolved.
After the officer signs off, you need to file the proof of correction with the court and pay an administrative fee, which is usually $25.00. I always tell people to make an extra copy of their citation with the proof of correction and have the court clerk stamp it to prove it was received. You should always pay fines using a method that can be verified -- such as a check or money order -- instead of cash.
If you don't file the proof of correction, you need to appear on your court date. If you don't, you can wind up with a failure to appear, as you did.
I would politely explain that you are embarrassed that you didn't realize there was still another step required, so you didn't file the proof of correction with the court, and ask if the judge will please allow you to do that now.
If the ticket was signed off before the court date you missed, the judge will most likely let you do that.
If you got it signed off AFTER the court date on your ticket, just make sure you don't claim you did it ahead of time. In that case, politely explain you screwed up, and the judge will probably dismiss the case if you pay the administrative fee.
Please understand that this is a general discussion of legal principles by a California lawyer and does not create an attorney/client relationship. It's impossible to give detailed, accurate advice based on a few sentences on a website (and you shouldn't provide too much specific information about your legal matter on a public forum like this site, anyway). You should always seek advice from an attorney licensed in your jurisdiction who can give you an informed opinion after reviewing all of the relevant information.
Mr. Marshall is right on target. However, I suggest you ask the judge to DISMISS your failure to appear (as opposed to you pleading guilty to it and the court suspends sentence), as failures to appear can be used against you in setting bail for future crimes.