I will ask you not to worry about the origin of class 11 topics in class 12 since if you have your concepts well developed in class 11 itself there is no need to constantly memorize the class 11 topics on class 12 all the you should take some gaps between units of class 12th completed when you should take around 3 to 4 days of and revise some topics very quickly from the class 11 syllabus for example after you have completed current is electromagnetism physics and before you start with wave optics you could just through the thermodynamics part or sound waves part of the class 11 syllabus similarly if you have animal physiology in class 11 and parts of botany and biotechnology class 12 then it will be clubbed up in between the competition of different units and regular practice of MCQs is also very important thing since the most effective way you will remember your class 11 syllabus by giving regular mock MCQ examination the time important to help you with your question selection and time management skills which will be mentally helpful for Neet examination