. . . . You may find if you defend yourself you'll be completely exonerated, on the other hand you may not and end up with a three-figure fine (I don't think you'll get a four-figure one).
While I have advised you to plead 'not guilty', I hope I made it clear that if the Company still choose that they wanted this to be decided in the Magistrates Court, then I would prefer you not to attempt to defend yourself. If you do, I and others can give practical assistance, but it's not appropriate for someone inexperienced to defend themselves against a Criminal Prosecution.
You could also try to write to one of the newspaper travel-help pages, explaining how you were told to board the train and now they are prosecuting you.
Indeed you could, and it might give you some comfort. But my view is that it is likely to distract you from the one simple fact that you need to remember, and is likely to demand your attention most at the one time that you need to summon the most concentrated mental focus on that one fact. The fact that you were given permission to board by a railway official who checked your tickets.
Media attention on you while you are attempting to defend yourself, and at the one momment when you need to be most attentive, is a bad idea.
Please don't put more demands on your valuable time and just stick to the simple strategy I've outlined.