It’s easy to score a 95% in Class 12 Boards ( Not sure about Commerce though ) Almost everyone gets a 95 in English , Fifth Subject ( Physical Education / C++ / IP ) can be handled easily . Coming on PCM If you solve last 5 year CBSE exams a minimum 85-90 in PCM is guaranteed rest comes with a little Hardwork !
All the best for your preparation
P.S. I studied for 20-25 days managed to get 95.4 %