Everyone makes occasional mistakes in evaluating the capabilities of others. Even should Prentiss prove insufficiently loyal rather than merely incompetent, that does not necessarily reflect upon you, particularly given your excellent performance today. (As well, your willingness to confess to an error in judgement speaks well of you; it has been my experience that the truly guilty inevitably attempt to cover up their actions.)

I will let Lucius know of your concerns, but I would not worry overmuch. At most I suspect he will believe you insufficiently practised at evaluating the capabilities or loyalties of others, and that is a skill best learnt over time.