As a lawyer, here's what to do... (NOT a California one, tho)
Take the boater course...get the certificate.
When you go to court, you will be respectful, dress well (not like me after four days of surf riding

), and you'll most likely talk to a prosecutor.
Explain (bring a picture of *your* ski) what you were doing. Point out that you were not near anyone else, you were not speeding, and you were not at any time out of control, although the trick you were doing may have looked it to the outsider. You may want to bring a picture of the trick to show the prosecutor during your discussion.
The prosecutor will most likely be interested in clearing the court calendar and going home, not listening to a dog and pony show. You'll most likely get an offer to a reduced charge. Pay the fine and go.
OR
You can be firm, and ask for a trial. You will get one, probably at the end of the calendar or another day. You will now be risking whatever the higher penalty is-and if you do this, don't do it unrepresented.
Most of the time a deal is offered with a fine, but I'm not a CA atty, so I can't state what specifically.
Here in NY, I'm so far unhassled.