Hello,

Well yes, covid-19 did impact studies of many students and it goes same for class 11th students.
Studying well in class 11th is very important because it creates the base without which you cannot do well im future. So, if you did not focus well in class 11th studies due to any reason, i would suggest you to cover all the chapters of class 11th again before starting for class 12 because it will not only help you to strengthen your basics but it will also help you in future when you will appear for entrance exams for admission for B.tech courses. There is no specific chapter on which you have to focus, you should cover up the entire class 11 syllabus that then only it will be helpful to you.

good luck