I am studying in Peru for my first years of high school how can I make the most out of it?

Not being hyperbolic here—getting a novel published by a Big 5 publisher is far and away a stronger accomplishment than what 98% of students are going to have in their profiles. I would relax. You have a long way to go if you're currently a freshman, and things might change again in a few months in ways we can't predict.

Okay schools will determine rigor by what’s available if you have no AP that’s fine.

I’d put volunteering off until next year as then it will be more impactful and you are in no rush. A general EC you might do is shadowing someone in your field in junior year but something you can do now assuming you have internet is make a blog and write about your major or any other topic.

The book thing is great especially by a big company as a freshman. When application rolls around I’d recomend you say it in quantative ways such as book name was published by x and it sold y copies

Also assuming your SAT is decent you should be able to get into most top 100 schools no problem excluding the ivies and ivy plus(Stanford mit nw rice etc)

Great job on the book!