Aeronautical Engineering

Seeing present scenario, computer science is far better than aerospace engineering in India. For aerospace, only service based companies are there to work and salary can never satisfy you.
Aerospace engineering requires a lot more analytical skills than computer science.
If a person is really interested in aerospace engineering and he is confident that he'll be the best engineer then only he should opt for aerospace engineering and after graduation, he must go for higher studies then only aerospace engineering can be beneficial.
While CS engineering provides a lot more opportunity. As we can see we are moving towards digitalization, everywhere we are seeing computers.
The scope of computer science is much better than aerospace.
But if you love flying you should definitely go for Aerospace as there will be much less competition as compared to CSE. All the best to your career!

B.Tech percentage must be above 60. Do read my article on this issue 60% aggregate for M.Tech admission.
Must have a wonderful GATE Score or Good All India Rank, or Good percentile. Don't get confused and afraid with 99 + percentile. Percentage is different from percentile to read more about it refer to How to calculate GATE percentile.
Also refer to Top Marks in GATE 2010 to get an idea how many marks you need to go to IITs 800+ score may be reasonably take you to IITs.
Be prepared to take another test at IIT for admission. Learn the basics of each subject, especially core subjects related to your engineering stream, as there may be a written test for admission to M.Tech if the number of candidates has close scores. Written test decision totally depends on the Department offering M.Tech program in IITs.
Things are not ideal for most of the times most of the students score 60% above in their B.Tech, but the real challenge comes when GATE cracking the GATE exam. If you have little less score and a great passion to get into IITs and that only matters to you, then you should continue reading.