As you Know Jee is one of the toughest exam and getting seat in IIT and even IIIT and NITS are the most prestigious and on the other hand toughest part. Though it's obviously not impossible, as you are aspiring and you have hardly 1.5 months for JEE mains 1st examination, I hope you have prepared and built the basic concepts of all the subjects. Start with NCERT books, which are the base for JEE main. Build a strong base of the concepts and theories from NCERT books. For practicing and advanced studying choose the right reference book. Try to solve a JEE mains model paper from the day being and don't miss giving an excuse. Try to attend mock test organised by different coaching institutes. Try to give 6 hours a day (2 hours for each subject) for studying or revising basic syllabus. Attend mock test from now and make the whole examination process clear.

All the best.