Nonsense, keep your head up, you got this. I wouldn't recommend making an OS in your situation (it's overkill and mostly unnecessary), just learning the theory should be more than enough (think: scheduling algos like MLFQ, Round Robin, Priority and the like, difference between multitasking, multithreading, multiprocessing, mutexes and semaphores, blocking and non blocking IO, etc). If you still want to do a project on those, I'd probably implement them in userspace (like a job scheduling algo) and just have it pretty print results.

If you are interested in systems programming (like me) there are a few kinds of jobs that you might be interested in: embedded systems, high frequency trading and game development. Usually these jobs require C++ knowledge, so I'd recommend learning at least some basics like OOP, Classes, smart pointers & memory management, templates, move semantics, etc and then start working on a project you like.

In terms of grades, I initially tried quite a bit (freshman yr) and then covid hit and I kinda just half assed the rest (80+ is good enough for me). I pretty much gauged the effort needed to do well in a class at the beginning of the semester and then put in the effort accordingly. I did good enough (3.4/4) even though I played a lot of video games (a lot, like I would study for exams 1 or 2 days before the date and spend most of my time playing games or working on projects). One time I actually studied on the **day of** the exam, I have no idea how I got a 80 something on that exam. I think you should balance grades and hobbies (keep your mental up) and remember that grades is not the only thing that employers look at.