Congratulations for securing 90% . U can even write JEE advanced as you have completed mains. If you clear jee advanced you can get IITs . Coming to your point 90% in jee mains is a very good percentile. You can apply for jee mains counseling which is commonly called as JoSAA counselling and u can get NIT's present across India that rank next to IIT's , NIT tiruchirappali is the best option for CS. For civil you can choose NIT Warangal