Hello Rocky,

NCERT is surely enough to score 60-70% marks in JEE Mains. As JEE Mains checks the basic concepts only which can be easily covered by NCERTs. But JEE Advanced is a bit different. It checks application based questions along with the basic concepts. You can always start from NCERTs and then go on for some different reference books available. Relying only on NCERTs will not fetch this much score in JEE Advanced. You can always test your performance by giving mock tests.

All the best.