@Flyverse if you enjoy Jack Reacher books, read Jack Reacher books! It’s not great literature, but it’s fun, and at the very least they will improve the speed with which you read in English. And that’s important, too.
As for the SATs, try some sample tests online. These are very different from any kind of tests you’ve likely taken in France. There are different strategies and “tricks” you can use to improve your score. And a large part of succeeding on the SATs is simply practice.
You might also google “xiggy’s method” on this site for strategies on how to study/improve on the SATs. Xiggy is a former university student who posts to this day on College Confidential. Many parents had their children successfully use “xiggy’s method” to improve their scores.
French schools are demanding. I’m sure once you get used to the SAT-type tests, you will do well on them, because the necessary knowledge is/will be there. It’s just a matter of making that knowledge work for you in an SAT-evident way.