Absolutely not necessary. If you think you have proper study plan and you are sticking to it and doing quality study at consistent pace, then it is perfectly okay. It is you who will have to study and work hard but it is beneficial to join any coaching institute to help you clear your doubts. For this you need not join any 5-star institute. You can join any good local institute that will help you with your doubts and guide you through the journey. You have to check with caliber, knowledge and experience of faculty who will lead you to success path. Few things you have to keep in mind and check before you join any coaching institute:
Professional and Disciplined Academic environment
Proper annual Academic Planner of Institute
Regular Planned Test Schedule
Full utilization of Academic hours only in Academics
Tests, Evaluations, and doubt clearing should be out of teaching hours
At least 2 hours utilization for teaching concepts
Interacting teaching and on the spot answering of your query should be there.
Timely completion of syllabus and plenty of revision and mock tests at the end of session.