In JEE mains last year the student who scored first rank got 350 marks. So you can expect your rank to be in top 100. 

I Hope this was helpful. 

Dear Aspirant, Congratulations on such a good score. At this marks your percentile would be around 99.8-100. So your AIR would be 1-174. At this rank, you can easily get into top NITS and IIITS. Good Luck. Previous year's cutoffs:-https://engineering.careers360.com/articles/jee-main-cutoff

Hi Lavanya,
340 marks in JEE Mains are amazing and really outstanding.
Depending on the level of question paper and normalisation between different slots, these marks can easily fetch you a single digit rank and most probably in top 5.
Hearty congratulations to you and get ready to see those coaching persons flocking around your house.
All The Best for the Future.
Thank You.

Hello dear, 

Congratulations for scoring 340 marks in jee mains ,your score is really appreciable. According to your marks in jee mains your general rank will be under top 10 ,you will be one of topper of jee mains, you don't have to worry about any NIT and branch you should head towards  jee advanced. 

Best of luck for your jee advanced.