Your mistake is thinking that a criminal misdemeanor is no big deal. The word "petty" might make you think it's not as impacting as it seems. But it goes on your criminal record and potential employers and colleges that you might attend will be likely know about a criminal conviction that is a part of your history. Now it is true that you will likely receive an alternative to the potential punishment - and you are very mistaken to call it a "scare lecture" which makes me wonder about your attitude. The
alternative sentencing you may receive is discretionary - it is not required by the court. Hence you want to be 100% sure that someone who knows the law, customs of the court and knows how to speak to a judge and prosecutor is available. If you do get alternative sentencing then it's possible that the charges could be dropped and you won't have a conviction on your record. These technicalities are important. And if your attitude makes a judge or prosecutor angry, I doubt your parents will know the difference between what is offered and what could have been offered.
It's not automatic. And there is a process. A criminal conviction doesn't go away automatically.
Bottom line is this - it's a crime that can stain your record for a very long time. Imagine you're interviewing for a job you really want and the person asks you if you've ever been convicted of a crime. Do you think they will feel good about you if you say "yes... but it was ONLY a petty crime?" I doubt they will feel the same as you do now. So get yourself the best help you can afford and ensure that your future has the highest chance of being clean from a stained criminal record. Good luck.