Am I at risk of criminal charges for shoplifting if it was handled by store security?

Yes, you are. A report will be sent to the DA's office for their review. If the DA decides to press charges you will most likely receive a letter informing you of your arraignment date. If, however, the report is poorly produced or lacks necessary evidence the DA could request further investigation, or they could decide to decline to press charges. I have heard of some stores offering a civil compromise, to avoid criminal conviction, in exchange for a very inflated bill. In order to avoid criminal conviction a court might allow a defendant to make the victim whole, or to compensate them for ALL losses resulting from the defendants action. Sometimes this can include the report filing and investigation charges. I have seen instances of an incident like you describe leading to a request for over $400 in "reimbursement." If you receive such an offer consult with a lawyer first.

Yes you can be charged, and under the facts you gave you will be charged. You need to get an attorney.

Yes, you can and probably will be charged with a crime. What can you do? Hire an attorney, unless you know how to effectively represent yourself in court against a professional prosecutor intending to convict. No amount of free 'tips and hints' from here or anywhere else are going to effectively help you in your defense, other than the advice to exercise the 5th Amendment right to SHUT UP and do NOT talk to anyone except an attorney about the case. That includes on this or any other web site or public forum. Most police and prosecutors will happily tell you that 95% of people convict themselves by trying to be 'helpful and cooperative', either during initial contact, questioning, interview or interrogation. If serious about hiring counsel to help you in this, and if this is in SoCal courts, feel free to contact me.

No you are not already charged. What will happen next is they will send you a letter demanding compensation, and they hope you will not contest it and just pay. However, unless a criminal charge(s) is filed, paying them won't do you any good. Civil litigation is very expensive, so they wish you will just pay and not force them to have to sue you (which will never happen for only $80). If charges are filed in criminal court, then the prosecutor will almost always demand restitution as part of any plea agreement. Right now, the best you can do is not to talk to anyone except your lawyer so you do not further incriminate yourself.

It is unusual that police were not called at the time. This does not mean there may not be potential criminal charges. As far as civil demand letters you are only required to pay the amount of the loss. If you are requested to pay more than the amount of the loss only pay it if you get a civil compromise agreement.

Yes. The best next step for you is to hire an experienced criminal defense attorney to help you as this is the best way to try to avoid a petty theft conviction. A petty theft conviction should be avoided at all costs as it can have long lasting consequences such as disqualifying you from future employment opportunities. The fact that you have a clean record and that the amount of the theft is relatively small are positive facts in terms of trying to avoid a conviction. I hope this answer was helpful. If you would like to discuss you case in more detail, I would be happy to do so. Good luck.