Still coming in on the late train. I'll more than likely just highlight what I was going to say that's already been said. Either way, best of luck. Well, here you go:

In a nostalgic look back, my time in HS went way better than I felt it went at the time. At the time, my perspective aligned with yours most completely. What I've learned since then is, contrary to franc's statement, high school's sole purpose is to teach you how to think; at least, to function in society in some capacity. What you do from there is on you.

(EDIT: Granted, there are many exceptions to the rule of those who "grow up earlier" or are just those that are standard deviants above the norm - either in IQ or PQ (Passion Quotient AKA Work Ethic).)

To answer your questions, both. On the topic of school and bettering yourself, I won't pretend I know your life plan, but whether you plan on continuing your education or not, do you work. Further, learn not to be afraid to ask for help. You'll be surprised just how much instructors can be willing to help those who work hard and are struggling. If you plan on entering college, then this point is all the more important seeing as instructors have near (if not) full control of your grades. If you don't plan on going to college, then learning to ask for help from a place of humility (not to mention learning humility) is a life skill that compounds beautifully with goobster's ending points. Too, volunteering is a phenomenal form of service to teach humility alongside building up a resume with the narrative of a community minded individual. To the end of bettering yourself, realize the multiple times getting a part-time job has come up in this comment section along side reading a damn book. With the understanding that HS teaches us how to think paired with 'the most free time of you life,' use that shit to your advantage. Making an earning was a massive confidence booster alongside engaging in thoughtful discussion during my time in HS. I don't have much to add on the point of body building that rthomas6 touched on, but that's no less important. My time on the physical fitness team can attest to his words.

When it comes to unique experiences in HS, on a shitty segue of being physically healthy, it's a help for both seeking out and getting laid. What I haven't seen which has been a huge help for me is joining a club. If you do all your work, get into your school's honor society. Run for a leadership position. If there's anything I'm reading from people writing "get a job," then it's 'take on role with responsibility'. Take the time to invest in a club with people of similar interest. It showed initiative when I was applying for my first job and taught me the elementary steps of human relations. It also gave me a playing ground to put into practice skills from therapy, but that's for another post. Clubs are the stepping stone for jobs in form of building a track record of accountability. If you plan on college, then leadership position(s) in club(s) easily takes care of the "extra curricular" slot. The latter paired with volunteer are routes to letters of recommendation to get your started with either a job or for college.

Best of luck. And I may be a bit bias, but I'd also add to the list to stick around. ;)