What is the best course of action for me to take at this point after I unknowingly committed statutory rape?

You are not a good decision maker. You committed statutory rape and then posted it here, on Facebook, and then confessed to the mother. Retain a good lawyer and do not talk to the police or anyone about this again.

In order to convict you of statutory rape under California Penal Code 261.5, the prosecutor must prove at least three facts. 1. That a male and female engaged in an act of sexual intercourse (any amount of penetration, regardless of how slight, constitutes sexual intercourse...even if there is no ejaculation), 2. That the persons involved in the act were not married to each other at the time (the fact that the minor is married to another or was formerly married does not excuse liability for this offense), and 3. That the alleged victim was under 18 at the time of the offense. The prosecutor may additionally have to prove that at the time of the alleged offense: 1. You and the alleged victim were no more than 3 years apart in age, 2. You and the alleged victim were more than 3 years apart in age, or 3. You were 21 or over and that the alleged victim was under 16. Defenses to Penal Code 261.5 PC Statutory Rape Charge include; You honestly and reasonably believed that the alleged victim was over 18. The types of evidence that can support your claim could include, for example: Statements made by the alleged victim that he/she was over the age of 18, His/her attire and general appearance, and Where you met the alleged victim (at an adult party or venue, for example). Unlike California Penal Code 261 rape, consent is not a defense. The reason that statutory rape is a crime is because minors are legally unable to give consent. This means that even if the alleged victim was a willing participant to the act, that fact will not serve as a legal defense to a California statutory rape charge. This is because the state believes that minors are too young to appreciate legally the consequences of their actions.

You have the right to remain silent. Only idiots talk to investigators/cops. Remember, no matter what you say it will be twisted around and used against you later.

You have publicly admitted a felony. Stop posting details online, take down your Facebook page, and get a defense lawyer hired to represent you pre-charging immediately. This could ruin your life if not handled properly.

Word to the wise: never post anything on Facebook that could get you charged with a crime or get you convicted of one. Also, do not under any circumstances speak to the police or agree to take a polygraph examination or submit to any DNA testing without first consulting with an attorney. This can be very serious and have life altering consequences so if you are charged you need to make sure you are represented by an experienced criminal defense attorney that specializes in or handles a lot of sex crimes or CSC cases.

Your word alone is not enough to convict you. They need the girl or other evidence to do so. Get a lawyer.

Two admissions from you. You need to (a) shut up and (b) secure counsel, in that order, and the less gap between a and b, the better.