Yes, you can complete your syllabus of 11th class in 3 months.

To start with your preparation you can make your time- table. You can set your daily and weekly targets.

Try to get a good hold on basics. Take help of NCERT books.

You can recommended other standard books as well for your preparation after completing your NCERT books.

Focus on the topics which carry more weightage in the exam. You can solve MCQs for your practice.

Refer previous year papers to check the level of the questions and you can prepare accordingly.

Good luck!!