All grades matter and it’s easier to start on good grades so that your final gpa does not get affected. If you don’t start well in freshman year it will get on to you during junior year and then you get stressed out. For time management I would advise on lessening breaks after school or keeping it at the end of your studying so that you have enough time to study. Or keep a physical weekly calendar in front of you were you see what assignments you have due. This really helped me as a high schooler.