Sir but the mistake that i made in choosing customary dress code.. will it cause any problem in xam hall??? 

No problem. But you should wear simple dress for exam..

Are you 100 % sure sir!! Coz i am in too much tension that if they cancel my xam for this mistake..

Dear,  Not 100 % sure, but i discuss with my senior, classmates and junior also. . They also agreed with me. .  Because no one candidate not allowed only for wrong option opt till now..  Only details should be correct. No can focused selection of options.. Only present is important.. Which drees you wear for exam. ..This is important.. And if you still tense... Then you can confirm with NTA and cbse..  And if possible you can correct this option during correction period.