The biggest problem is that you think you did well. The truth is, you never know. Ask any recommended candidate what they did different from others. They would not know. No one ever knows. That is what SSB is all about. OLQs are the basic necessity, everybody knows it.
So when you think you did well, that is where you are mistaken. At least according to the Board you lacked somewhere.
So first things , accept that you did not do well. Do not take it to heart but do accept this reality. Only then you can expect thoughts on improvement. If you already think your performance is flawless, you leave little scope for improvement. One reason for failure this time could be that you took your preparation for granted. It is really difficult to judge..
Honestly think along the lines "what I could have done better". Do not be superstitious. Self introspection is the need of the hour. But first of all, start believing that you can do better and the last performance was not your best.