Still too long.
You can make it short and to the point hoping a human reads it. A person will never actually read that much, they'll just scan it. They're devoting the same amount of attention to each no matter how much you write, so zero filler is best.
Or you go long, to try and jam in many keywords as possible if you think it has an AI filter before it gets to a human, which is a thing that happens. And often no human will ever read the cover letter in that scenario.
I've known people that apply both ways to every spot. But there was also a guy that applied to where I work and got on the same interview list twice because he did it and they only noticed because the same phone number was on the list twice.
Like, you're talking about taking college courses in highschool (which is great!) but also means the types of jobs you're likely applying from wont have the AI filter, so you want the short and sweet version.
It's a numbers game. Apply to fucking everything and understand HR is going to have a mountain to sort thru for anything remotely decent these days. For a lot of spots they're just glancing at 100 applications and picking 10 for interviews for one spot. You want your cover letter distilled to just enough to get your resume looked at to make the cutoffs for interviews. You're trying to have the interview before they look at your resume.
Edit:
Also, for asking for help on editing/writing, it's best to copy/paste the text.
That way someone can highlight and quote parts, with a screenshot they have to type it out and that barrier to entry might dissuade someone from chiming in with advice.