No offense intended, but if you are having troouble figuring out whether the plea was to an infraction or a misdemeanor and do not understand how to fill out the form, you might want an attorney.
Keep in mind that there is no true expungement in California. All that happens is a notation in the file that you were allowed to have the case dismissed. The record of arrest and conviction remains for all to see and you still have to report the conviction when applying for governmental employment or issuance of a license other than your CDL.
The above is not intended as legal advice. The response does not constitute the creation of an attorney client relationship as this forum does not provide for a confidential communication.
It sounds like you need a little help, although it is a very simple and straightforward process and the court has to grant it for you if you have successfully completed probation if it was a misdemeanor or after a year if it was an infraction. Question: Were you placed on probation? If so, it was a misdemeanor. You can always call the court and ask them if you were convicted of a misdemeanor or an infraction. Anyone can file the petition for you, but there is a filing fee that must be paid or a fee waiver process if you can't afford it. Lawyers' prices vary.