No, with 63% you are not eligible to get seat in NITs/IIITs/GFTIs and BITSAT as well so it would be better to give improvement exam to get the required percentage like for jee main you will have to get 75% or you should be there in top 20 percentile and for BITSAT 75% are required and 60% each in PCM should be there. To appear in improvement exam, you can simply register on CBSE wesbite or you can get the offline form from your school as well.

Hope this helps!!!!