@dnhk it seems you just were not fully prepared in my opinion not to mention based on some of your responses, seems your english is still not fully polished as well these with accumulation of a lot of "I don't remember" and your mere presence in the United States was to study meaning improve polish your english since that is the native language may have just irritated the officer. Remember many times when these officers are just not having a good day their easy out is recommend you withdraw and if you agree that is one less file they will worry about.
My biggest issue are certain key information you do not remember, as an immigrant and i believe many people on here will agree with me are we depend on accurate dates and information memorized whiles still at the mercy of greencards that is no brainer. You may want to do some more due diligence in understanding ur entire history and dates. I know you are seeking legal assistance, but an attorney will not answer some of these questions for you, so even retaining one with you not prepared or not knowing basic simple question will lead you to the same path. I recommend listening to some of the members, getting your A file and going through your entire history from when you applied for F1 all the way down to current. You actually are lucky they asked basic simple questions, many have been asked much more headscratching questions.
Best of Luck