srbose
Did you file your I-485 petition, after the arrest incident and you forgot to mention the arrest? Or, are you saying that I-485 was filed before the arrest incident and you just didn't get an opportunity to file the I-485 with the right answers w.r.t your arrest?
Please note that in your case, there are no charges and hence no conviction. Since the Judge dismissed the case, I strongly feel that it was dismissed with prejudice and therefore the State did not prosecute you. Ipso facto, you are not covered under the Criminal Justice System.
However, if you had not answered YES to the questions related to your arrest while filing I-485, it may be a precarious situation because of possibility of committing a penalty under perjury. However, I would still say that when called for I-485 interview, they will explicitly ask you to verify if all the answers are true in the form, at which time, you may correct the answers depending on what you already submitted. I do not think they will punish you, given the fact, you had on your own will had called the police and submitted yourself to the fullest extent of law. Hence the question of a crime of moral turpitude is not applicable here. In a worst case scenario, if you are cornered for suppression of truth in your I-485 form, you can tell them the true fact that you were not convicted and no judge had ordered any restrainment of your freedom to warrant an affirmative answer to those questions. Please note that whatever I have posited in bold have legal repercussions and should not be read very lightly in a pure literal context.
As I always used to say to others who write to me privately about their fears w.r.t having a brush with the Criminal Justice System, I plainly tell them to just face the interview with aplomb without trying to conjure up all the worst case scenarios. Focusing on the present wins the future you are afraid of. Friend, let me tell you plainly, that almost all of them (at least 10) reported their success stories with me. Only one guy, whose criminal case was going on for 2-years wasn't able to take up the financial and mental stress anymore and finally decided to leave to his own country. And more than those stresses, he felt lonely, isolated, bitched and condemned by many in the society and his own close-circles that he couldn't take it any more. Why I am saying this is not to just make you feel good, but to be pragmatically optimistic about your case. While I exude hope, I do not hype it up only to make you feel hopeless later.
Just as those ten folks, you will also be successful in your pursuit, if you can only patiently await your turn for interview, without conjuring up all worst-case scenarios. Please note, law in this country is equally poised for relief and remedy to both the immigrants as well as INS. If you are convinced that INS has more teeth to take you on, I am even more convinced that I have more teeth as well to seek remedy from those very same laws. This is a great country and you can join me in reiterating the motto of the State of South Carolina: Dum spiro, spero. (As long as I breathe, so long will I hope.)
Your dreams will come true. Just have a good night sleep. God bless.