> ... exam ... determines what college you get into.
Noted.
> I performed terribly on my exam so I could only get into very mediocre colleges.
Noted.
> ... will be trying again but I don't think that results will be much different this time either.
So you are demotivated, and despite the gap year, you feel you won't do any better.
> ... the mediocre colleges here are straight up garbage. The quality of teaching is abysmal.
Noted.
> I feel like I'd be better off learning things on my own than going to such a college.
If you are demotivated, why do you think you will do better studying on your own? Will you be able to create and maintain the motivation? What is it that motivates you?
> There are so many amazing CS courses online that I can use to teach myself.
Yes there are, but the ones worth doing require significant amounts of work, and maintaining that level of commitment is hard. Perhaps you need to work out why your preparation for your exams is going poorly, try to get to the root cause of your lack of motivation.
> ... for most jobs here, a college degree is an essential requirement.
Then you need a college degree.
> Any advice would be deeply appreciated.
So:
* You need a college degree;
* The colleges you can get into are rubbish;
* You feel you could study on your own.
Based purely on that it would seem that you should go to one of the colleges, meet their minimum attendance requirements, study on your own, making sure that you cover all of the material that will be on the exam, ace the exams, get your degree, and move on.
The fact that the teaching is rubbish will be irrelevant, and the existence of the exams will help to give you focus on your study. You will be forced to cover even those things you don't really like, which if you do solely self-study is a danger.
Take control of your own learning, but allow it to be guided by the college's curriculum. You will get your degree, be experienced at self-learning, and have a complete and well-rounded education.