As a person who not only has school but also has usual work and high paying commissions I know what its like being stressed at a young age.
I'm not sure why you'd worry, unless you didn't do your work or something and you know you'll get a zero. As long as you stay on task you should be fine and have enough time to relax afterwards (like what Shiro said, games, videos, etc. personally I prefer music and game modding). Also, take advantage of weekends more than anything. They only become more precious as you go on in life.
If you need help with some school work I'll try to help. I'm not a straight A student unless its graphic design stuff but still...
