Your a 16 year old boy not a Saint I don't think God would have a issue with you wacking the cherry tree every now and then and masterbation does provent prostate cancer in men so it is healthy for you.
A list of twelve major sins named in the New Testament and the Apostolic Fathers' writings. They are all various transgressions of the Ten Commandments:
Murder
Idolatry
Sorcery, magic
Avarice
Theft
Envies: jealousy, greed, love of vain glory, hatred
Lies: false witness, perjury, hypocrisy, slander
Spite: anger, rebellion, argument, perverseness, bad temper, gossips, insults, injustice, deceitfulness.
Pride: boastfulness, vanity, arrogance.
Fickleness and insanity
Drunkenness and intemperance.
Impurity: adultery, the practice of homosexuality, fornication, pederasty, concupiscence, impure language, use of pornographic materials
so you watched porn go confess to your priest but as you can see beating off is not a sin and is perfectly fine in the catholic church as long as your not looking at porn while you do it .