Hi there!
First of all, please don’t panic. You will NOT be going to prison over this. You have been reported for prosecution. This means you will receive a letter within 6 months asking for your version of events (once you do receive this, please do post it on here (personal details redacted) so I can help advise the best course of action.
After you respond to this letter, there are two possible outcomes:
1) TfL will offer an out of court settlement to close the matter. This is a sum of money (generally the unpaid fare plus £100 - £150 to cover admin costs) to close the matter. This feels like a fine but isn’t and is simply a sum paid to TfL to keep the matter out of court.
2) TfL pursue a prosecution in the Magistrates Court. The outcome of this depends which law the prosecute under (they can prosecute you either under the Railway Byelaws 2005 or the Regulation of Railways Act 1889).
A Byelaw prosecution is “spent” immediately and will not appear on a standard DBS check, whereas a ROR Act prosecution will show up for at least one year.
On top of the ticket cost and the admin fees, the courts would also impose a fine.
It is entirely possible to get option (1), but it is imperative you reply to the letter they sent in a constructive and apologetic manner to maximise the chance of this outcome.
I also recommend you post a thread on here with your case:
https://www.railforums.co.uk/forums/disputes-prosecutions.152/There are many experts who have studied rail fares and contract law on here and specialise in cases like this. They are happy to offer their advice (free of charge) - so feel free to use their assistance should you wish