It is a great question. I'm now almost retired and I've thought about this a lot and never solved it perfectly.
I don't think there is a single tool that answers your question.
I would suggest looking at Gantt charts for the high level view of your tasks. You could make one for the semester with just the major dates (exams, paper due dates) plotted. You can get an app or just make one in Numbers by filling in cells. I never made it work but I liked the idea of a timeline to visualize the upcoming few months. Look up Gantt charts on wiki.
I would add a lot of information to the calendar app. Even without alarms it is great to visualize what you are committed to. I also like the idea of using alarms in Calendar to remind you of upcoming events. I find this very helpful. It is nice to set one alarm for the day ahead and a second for maybe one hour ahead. I used this a lot for business trips to keep track of what I needed to do hour-by-hour.
I would use to-do lists for just the things you need to do in the next 48 hours or less. In the evening you could make a schedule of what to do the next day. At then end of that day review the list and figure out how to manage the items you didn't get to. The worst thing is to keep a permanent to-do list which gets cluttered up with things you will never get to. Try not to add big items to the list (write a term paper). Just add things you can complete in an hour or so.
If you load up a Gantt chart with too many details it becomes useless. On the other hand, if you load up a to-do list with everything to do in the semester it becomes unwieldy. You need it just for things you can do immediately.
A problem we all run into is estimating the time needed for any task. I can schedule 30 minutes for lunch but how long will it take me to learn the current section in math or write a good paper? This is the heart of the problem. You need something like a schedule to guide you but you need the flexibility to adapt to your humanity.
Aother suggestion unrelated to this. See if you can find a study coach. Not a tutor. Just a senior person who knows your school whom you can talk to weekly who will help to keep you on schedule.
One final suggestion, keep a simple journal of your activities. I keep a simple text file. Every day write down at least two or three sentences about what happened. More is better if you can manage it. You won't appreciate this till much later in your life.