A lot of info in textbooks is supplementary information that may not be necessary. You will get a much better idea of what you should know once you go back to school and your teacher begins teaching the content, as they will teach only what is necessary. From this, you should be able to deduce what info in textbooks is unnecessary. Often times, it can be difficult to go from purely the study design as it can be unclear to what extent you need to know each dot point. Summary notes can be useful if you prefer to go off a shorter, more succinct version of your textbook rather than sorting through all the unnecessary information it contains. Textbook explanations go into detail, however, and can be useful to solidify your knowledge on difficult topics, so I advise against completely abandoning it. You are doing fine, and you'll be much more confident about what you should/shouldn't know once school starts. Good luck!