Monologues?

How many lines should a monologue be? I've looked online but they all seem to be written to fit an allocated time slot for an audition. I'm writing one for a GCSE controlled assessment rather than an audition so should it be longer?
Also this is the first monologue I have ever written so I'm not entirely sure whether what I have written is actually a monologue. Does anyone have any examples of good monologues which would help me? Thanks!