Im at class 10th and I know that I need to prepare for jee mains right at 11th but my doubt was are the topics of ncert and jee same if not what are the chapters which are not included in ncert And if I prepare for jee then should I also prepare separately fo kcet exams

dear ayan 
i recommend you to join cbse in class 11^th , that will help you to gain maximum in jee mains exam . 
and there are few topics that are not in ncert , like in physics u need to know about the introductory part , like integration , derivative , at first , but for that u have to look upon h c verma . 
and in maths 1-2 topics are there ,, but that will not matter much . 
so, majority of the ques are based upon the ncert tesxtbook concept , but not copied . 
AND , about kcet exam , u need not to prepare for that separately , they also have ncert based ques from last 2 years . 
hope it clears 
regards