Many students have this problem and it’s okay.
Forget the past focus on now .but now you have to speed up and need focus.
1.get rid off unnecessary material.
Many book’s you study and waste your time have no values if it will not ask in exam so following ncert and few books solving previous year paper and giving some test is good,so you can revise them effectively.if you visit previous year questions it will be best for you to get some idea about exam leval.follow 80/20 rule.
For physics remember all the formula and start practicing questions.
For biology read ncert and for chemistry read ncert with MCQs.
Don’t worry about questions who asked out of ncert .there is no worth of time solving those questions and “get rid off distraction who wasted your previous 6 months is most important.”
2.get some help