IIT

For second attempt, ask yourself why you did not succeed in the first attempt, if you genuinely believe you can improve on that reason. For example, if you were not well on exam day, try again. Please remember competition increases every year. If this year was tough, next year will be tougher.

You can see the cut-off of the previous years by clicking the below link and have an idea how the scenario will be this year
https://www.shiksha.com/design/industrial-product-design/exams/uceed/cutoff.

There are other colleges, considering the cases like IIT ranks around 10000 and above you can attempt for two major Chemical and petroleum degrees from IIPE, (mentor by IIT KGP) Which is the 3rd year of the college. RGIPT, Raebareli, which provides degree in Petroleum but, there are likely to close around INR 15 k to INR 18k as well. There might be new addition, in some university seat or Scholarship based on JEE Advanced Rank. Read Advanced Brochure.
There are a few International colleges in Singapore that consider Advance Rank along with IISc Bangalore for it's Bachelor's Programs.

No, IITs do not provide any commerce related courses. They only offer B.Tech, M.Tech, MBA and Ph.D. programs.

75% marks is minimum to get IIT.

What you have to do is check out whether you are ready to face IIT or NIT entrance exams, if answer is yes, then go for it. Choose next IIT classes in your city give the entrance exam of that institute. Coaching is the only way to prepare yourself for IIT. So, Be ready to face challenges. Study hard. It is key for success to crack IIT. Best of Luck.

When you are in different branch other than computer Science in engineering, you can study Computer Science side by side as per your interest not going for the syllabus. You can learn programming languages by yourself, there are lots of online classes available and you can go for coaching centers also learn the programming languages.

Hello Yogesh, I am afraid 120 marks in JEE Advanced are rather low for getting admission in an IIT.

There is no role of class 12th percentage for admission in NITs and IITs only a minimum of 75% is necessary. So, if you have got 75% in class 12th, then there is no need to drop for board instead of this you should focus on JEE Main and Advance exam.