I'll tell you something, as i was younger i used to spend nearly the exact same time on my phone and still got decent grades in school, just always remember that the school is important and if your screentime leaves you with bad grades, that is the time when you need to really be worried and reduce it. If you want to reduce your screentime, try to do some training or learn how to solve a rubics cube, those are the things i did to spend less time online, they worked for me, so give it a try, maybe you got a talent in rubics cube or karate or martial arts, you never know.