I think he implied that he hasn't been paid yet. In that case they wouldn't discover it until they ran the prepayment audit, where they *definitely* would.
I can only see good things coming from confessing.
a) When they run the filter they will find out anyhow.
b) You may have the chance to save your account this way, especially by pointing out that you haven't done it since April and deeply regret it. They are people too, and will appreciate your advance honesty.