Hey dude 340 is such a high score. You can achieve it by hardwork but it is too difficult to score 340. You can give JEE Advanced only two times consequently. 1st during your 12th and another attempt during one year drop after 12th. So no IIT will accept two time dropper. But no need to worry you have lots of options trough JEE Mains. There are many good NITs better than IITs accept JEE Mains marks and Boards marks. So if you have good AIR in JOSAA. Then it would be very easy for you to get good college.
Best of luck