Not trying to scare you, just to impress upon you the gravity of the situation and the possible implications/consequences. Your deviation into Class B is recorded on a radar tape. As I understand it, those tapes, especially deviations, get independently reviewed by a group located in Dallas (QA/QC). The controller gets in trouble if he/she doesn't "report" those deviations to his higher-up (taking away the discretion). Basically, a paper trail of little "reports" is created and some middle-manager FAA/ATC drone very well may just forward it to the FSDO because that's what the rules say he's supposed to do, even though the guy you spoke to said it was "over." I can tell you from experience that "this is the last you'll hear of it" may only mean "this is the last you'll hear of it FROM ME."
At this point, these are nothing but lessons for the future. It's not really your fault, instructors, mostly due to their own ignorance/lack of training, do a ****-poor job of making sure students are prepared for these kinds of situations. Nobody tells you the right way to handle being told to call ATC (nor does anyone tell you that you're under ABSOLUTELY NO OBLIGATION to actually call), and the gut-level, human reaction is to call and try to talk yourself out of it or beg for mercy ("If I can just explain what happened they'll understand...). Unfortunately, that reaction is rarely successful anymore because of the aforementioned changes to internal ATC procedures.
Again, not trying to scare you, but it's important that you (and others) understand the process and the risks. File your NASA form, have a beer, and don't worry about it unless and until a letter shows up in the mail. If that happens, find a local aviation attorney to help you out (or call AOPA Legal Services if you pay for that).