I have been charged with 3 counts of abuse of position. I'm so scared, what sentence will I get?

I worked for a rail company and loaded a rail discount of 75% onto two oyster cards in January 2011, one for myself and one for my wife, after hearing people were doing this at work. I stupidly gave into temptation. This probably saved us about 55 pound a month. However, in April, my colleague asked me if I wanted an annual travelcard for free. I said yes and gave this to my wife who was using it from April. She got caught with the ticket on May 23rd and they subsequently found her oyster card. I went down to the police station and admitted to them that I loaded the oyster card discount and issued the ticket (I didn't want to get anyone else in trouble). They arrested me and found my oyster card as well. My wife is being charged with 2 counts of possessing a fraudulent article. She did not know she was not entitled to these tickets since she knew I worked for the underground plus I get 75% off all over travel. Hopefully, she will be OK. The police raided our house and took our computers (even my housemate's laptop), phones, documents, passports and iPods! Obviously, suspecting some deeper scam. It doesn't go further than me using my ticket machine to put a discount on 2 oyster cards at work. I so frightened because I read other cases of abuse of position where people have taken thousands of pounds from other people and been imprisoned. I am good person who made very stupid mistakes which I regret so much. I have lost my job as a result and I fear others will in the future. Do you think I face prison time?