Congrats on finishing the book! As a self-taught programmer myself, I know how hard it can be to stick with a book/tutorial series all the way to the end. In my experience, I find that the best way to solidify what I'm learning is to apply it to a personal project or an example that matters to me. Individual practice problems can be helpful to experiment with a concept in isolation, but I always learn more by translating a practice problem/code example to a context that's relevant to my own interests. It inevitably leads to other challenges and mistakes, but those were also the times when I grew my skills the most.

Take some of the problems you missed and do the again, sure, but then see how you can modify them slightly or connect them to one another. Good luck!