Thanks. Is it any more likely that I will get a fine than a summon to court?

Hi, I got caught using a child ticket on london underground!? It was such a stupid act!!! I will regret this forever. I decided to do it because I forgot my railcard today (which usually gives me discount) and the normal day travelcard is expensive . So there I got caught by the inspector and I had to give my name and address and real date of birth (as I tried to lie initially ). The thing is, he said that all I would get would be a letter telling me not to do this again. Is this the truth? or anything more serious could happen to me? Btw I am 18 years of age.