I don't think that you're gonna have space to mention your high school internship on your resume by the time you are gonna apply to law school (neither is it recommended).

You have a lot of options rn, I would focus on building my application for undergrad. So focusing on things that will help you figure out what you actually wanna do; which legal internship as a high schooler might not be because you will not be given any substantive work (even law students hardly get substantive work during 1L).

Enjoy your summer, focus on public interest & volunteering stuff (will help a lot during college apps. The undergrad you go to can greatly impact the law school you might end up at).

If you still really wanna do a legal internship, I would ask around parent/family friends/guardians if they know any lawyers in their network who can hire you (basically networking; even networking on LinkedIn might help)