Project Euler is without a doubt the internet's best repository of computational problems. At present (9/3/20), I've solved 45 out of 723. Beat me!
Another great source of code puzzles is Advent of Code.
Perhaps you'll want to work through another book. The Structure and Interpretation of Computer Programs by Abelson and Sussman is one of the best. The language is Lisp. (Hope you like parentheses! I got tired of them and switched over to Python.)
How to Design Programs by Felleisen, Findler, Flatt and Krishnamurthi is also great. Again the language is Lisp (specifically the Scheme dialect of Lisp).
Computer Science: An Interdisciplinary Approach by Sedgewick and Wayne. It's the text I use in my AP CS A. Truly excellent. The language is Java. It made my love statically typed languages.
I mean math that will be helpful to programmers.
Definitely spend time with Knuth's Concrete Mathematics. It's a classic.
Perhaps the best I can give you if you wish to continue on in CS is to make something. Make a game. Make an app for your phone. Whatever. Find out what tools people use and give it a try.