15 year old minor caught shoplifting in washington state?

i was caught shoplifting from JCPenney yesterday by the LP people. pretty much i stuck a pair of shorts and a shirt in my bag in the fitting room and tried to walk out. the LP guy stopped me about 10 feet out of the store and asked me to go to their little back room. He asked me if i was shoplifting and i figured since he already knew i admitted to everything. I know you might think it was stupid to confess but it felt like the right thing to do =_= anyways, i signed the confession, they called my parents and called the cops. a cop came in and "arrested" me, he pretty much patted me down, read my rights and told me he was gonna forward his report to the prosecutioner's office or something. i live in washington state and the total cost of the merchandise was only 45$. this is my first time offence, i am 15, have a 3.9 gpa, AP classes, sports, etc. I know it was a dumb*** thing to do and i really feel bad about it. i wrote a letter to the management at the store but what happens next? do i get communtiy service, fines, classes? and will it be expunged when i turn 18? help?