Showing up and pleading guilty is the worst idea you could ever have. At least use the services of the public defender or a lawyer. Why are you planning to just let the government do whatever they want with you?
My standard disclaimer: I am not offering legal advice, assume I do not know the law in your state and that I am just making suggestions for starting points for when you do speak with an attorney. Do NOT rely on anything I write and contact a lawyer in your area immediately after reading my posting.
Of course you can plead guilty at the arraignment. The real question is should you? And how do you make sure you get the best disposition possible given the facts of your case?
The only way to answer those questions is to speak to a lawyer. If you can't afford one, you can ask for a public defender to be appointed to represent you. You need a lawyer to read the police report, get the facts from you and negotiate with the DA. Your lawyer will be able to tell you if pleading at arraignment is best or not.
Don't be in a rush - do it right and protect your rights.
I'm glad you've taken steps to iron out your life. But why saddle yourself with a criminal conviction record without even letting a lawyer take a look and see if they can prove their case. It DOES happen that people who committed a crime get let go for various reasons. At least sit down with a lawyer and get a free consultation to get a lawyer's input. But I do think you need to get the police report first to know what the case is about. Does not sound like you remember all that much of it. You get a copy of the report when you go to the arraignment most places. Be patient. This is NOT a time to be in a hurry. Have you any idea how hard it is to find a job with a criminal record?
You really should consult with a criminal defense attorney in your area. Pleading guilty at this ealry stage could quite possibly be the wrong thing to do. However, this determination can only be made by an attorney. If you cannot afford an attorney asked to be represented by the Public Defender. Good Luck!