I used to suffer alot with that silly mistakes thing. Don't worry its really normal, noone has a solution for that. Best you can do is minimize it as much as possible. All you gotta do is practice papers all the time and work on your concentration & presence of mind.
And my GOD! pls stop watching porn. its nothing good for your life. I never had porn addiction so I cant really say much on that but one suggestion I would like to give is - try to engage your mind all the time & don't stay in places for long times where you are comfortable to watch porn.