Koco,
Sure there are the horror stories, though in the vast majority of these types of cases the FAA just wants to know what happened, and if applicable, that you learned a lesson, and be reasonably assured it will not happen again. They will generally take the situation and your experience level into consideration as well. When I have been given the number to call, I chose to call and be forthcoming, polite and deferential. On occasion they just want to ask a question about your operation or why you did something in a particular manner, even if there was no violation. I've had that also. I have had to call a few times, over many years. It worked out fine in each case. If you do not call, you are then essentially/effectively forcing the FAA's hand, which can trigger a formal investigation. That's typically when things get ugly. I am not making any recommendations, except to send the NASA form, just sharing my experience. Good luck!