Your schedule looks okay to me. I've had a sim who took 4 classes, the soccer team, the Brainiacs, the Bot Savants, and the Spirit Squad. He had enough time for all of them and even found time for some of the City Living festivals. He graduated with A+ in all classes and the top level of the soccer team. However, you have to decide for yourself how much you can handle. There's nothing wrong with taking a lighter load.
All of the sims I've put through university took 4 classes per term, they've always gotten A+ for every class, most of them have belonged to at least one organization, and some have even had jobs. Sometimes I had to choose between activities, and sometimes I had to skip activities in order to sleep, but usually there was enough time for everything.
Learn the Research & Debate skill. Level 3 will reduce your homework time. Level 6 reduces the time for term papers and presentations.
Use the Study Spot lot trait. Do your studying at the Laurel Library, which already has the trait, or give the trait to another location.
I usually had my sims in the Focused mood for homework, classes, term papers, and presentations but I don't know if it actually helps.
Join the organizations that contribute to your major and reach level 2 in those organizations. You'll get extra credit for attending their activities once you've reached level 2.
- Brainiacs are my favorite because they give extra credit for ALL majors.
- Bot Savants give extra credit for Computer Science, Physics, and Villainy.
- Art Society gives extra credit for Art History and Fine Art.
- Debate Guild gives extra credit for Communications, History, Language, Psychology, and Economics.
You can only join the organizations that belong to your university. I don't think the Spirit organizations help academically but they are fun to participate in.