Train Ticket?!?!?!? help !?

Today i took the train , and i got a 150.00 ticket for not having a train ticket... the thing is , i did have one, but i forgot to validate it. so i still got charged. Im scared to tell my mom about it. she will get very mad, for one, i was suppose to be at school when this happened, and for two, we are having money problems right now. so i cant pay it alone. What would happen if i didnt pay it ?! I am 16 years old... thank you guys. serious answers only . i need the help . thanks again.