There is nothing wrong with being prepared and rehearsed - but some people don't seem realise what that really means.
Interviews arn't all about knowing a correct answer, its about how to approach trying to answer.
Also, blaming poor interview performance on "over-rehearsal" is just nonsense. If you did badly, its more likely that you were confused as to what to say, when, in what sequence and how.
IMO, that is what you need to improve on - and quick