Well, youngster, now you get to the wonderful world of PERSONAL RESPONSIBILITY. If the police don't show in the next 15 minutes or so, you probably won't hear from them. If they do show up, shutup. You have the right to free speech, and that includes saying nothing at all. Tell them you have nothing to say until your parents and a lawyer are present. You might get arrested, and the gun might get confiscated, and you might get bullied by the authorities. Keep your mouth shut. You can expect your Dad to apply a 55 gallon drum of asswhup all over you. What if you get into trouble? You're already in deep doo doo. Wait until your father gets home! And, oh by the way, that "accidental discharge" crap doesn't fly too far. You loaded the gun and you pulled the trigger. The gun didn't actuate by itself.
Edit: Now that I've seen you're explanation (Daddy left, Mom's going to Canada, and big brother is working) I'm calling you out on this. I say your entire is bullshit and this never happened. In the unlikely event it did, you're going to find out more than you want to know about "beneficial possession of a firearm" in Pennsylvania. Welcome to the legal system, or piss off if you're a troll.
Man up. Dad will likely beat your a$$, but it sounds like a butt whup is just what you need.