Of course not. JEE is a national level examination where students across the country compete together so obviously the exam level is going to be of a certain height, a height of course more than the CBSE boards. There are lots of tricky questions asked in JEE MAINS AND JEE ADVANCE is double the toughness of MAINS exam. So prepare for JEE well, and automatically your boards will also good.. But if you do vice versa,  then you face problems for sure that's what I feel.

Best wishes. Thank you.