how should I manage my time in highscool?

Honestly high school won't take as much effort as you think. Unless you plan on getting a ride into an Ivy league school or something then your grades don't even matter that much.In honors classes you can at least get a B in with minimal effort (i.e. showing up 75-80% of the time and completing all major assignments). Most colleges have shockingly low standards to get in so unless you're aiming really high I wouldn't worry about it. For whatever reason people like to tell you that it's way more important than it really is.

If you do however plan on shooting high (like Ivy league) then it's pretty much a go hard or go home situation. My friend was valedictorian of my graduating class, he had perfect marks (he'd only ever missed one minor assignment which was completely my fault) and he still didn't even get into Stanford. My best friend from another school however did get into Colombia with her valedictorian status. Both of them had participated in at 2-3 different sports and 2-3 different clubs. It's more advantageous to join clubs then it is to get jobs when trying to impress colleges. Both of these friends did nothing but go home and do homework/study when they weren't at practice a game or a club meeting / event.

Outside of getting into a really good school, the things you do in high school really don't matter for anything other than your personal memories, so it may not even be worth your time to stress over.

I promise it's easier than people are making it out to be too though. I graduated with high honors and the only time I ever studied was walking into class, I never spent more than two hours on a high school essay (they're rarely over five pages long so you can knock em out in no time).

I would check your syllabus for how your teacher weights their grade too, because some teachers will really weigh attendance, but if the class is trying to ease you into college around 60% of your grade will be based solely on your tests. Just focus on what's weighted more. So if you have an essay and math homework due in two hours, complete the essay first seeing as it would be a bigger assignment and don't stress that some little ones slip through the cracks.

Going to a new school can be really scary but trust me it's not that much harder! You have to put the time and effort in, just think about what you can achieve! I'm not saying you have to be studying 24/7 but you do need to work hard! You could try and make a homework timetable, don't worry you'll still have time to see your friends or go dancing. Good Luck!:)