I cleared jee main with 67 percentile and qualified to jee advanced as I am sc candidate but I decided not to write jee advanced as I got maximum 40 marks in jee main and and I wished to join iisc but after seeing cutoff I thought I cannot get that high rank. tell me whether my decision is write

Dear student,
Don't regret that you have got less score in jee mains. Less score depends on various factors, like fear of giving exam at the centre, the high peer pressure, continuously thinking what happens if i get less marks ? what will i do ? what will my parents say?
And also you will get less score if you have not studied well. On the other hand it may happens that you have studied well but not practiced much questions so your confidence level will get low and you will get low score or marks.
And never give up, give the jee advanced exam with full confidence and just be normal and think yourself as a pro. Never lose hope. If you are thinking about iisc then dedicate you while body, mind, soul for iisc. Because what's done is done and your cannot change you past, but you been change your future with your own hands with dedication, with hard work and never think that you can not do.
Every man or woman on this earth can achieve any thing in their life if they want to.
Also, you must give jee advanced exam without any fear or pressure.