Not a sin you can keep doing it or stop up to you :-D
I am 17 too. I ll share my experience with you. There used to be a time , where I would see porn every single day and masterbate alot. It used to be a habit and I was extremely addicted to this bad habit. I used to masterbate like around 3-4 times a day until i was satisfied. But I came across this guy who is 5 years elder than me , I was 14 that time and he was 19. He told me to stop seeing porn, it's bad. I asked him why and he said that 1)- it destroys the image of women. 2)- You don't respect women by seeing porn . Most of the pornstars on those websites are women. 3)- it's quite addictive 4)- It ruins the image of sex. Passionate sex is not the type of sex you see in porn sites, it's rather wild sex. i thought of this and I realized that this bad habit must be stopped. After a while, I had this crush on a girl, So I forgot about porn since I had her company. Masterbation is something which is very difficult to stop. You will stop it when you have a GF. Hope I helped you.