Class 11

First, equip yourself with the understanding of Fashion designing. Start following the works by established designers and read some about the field. There are multiple ways to get into this domain I.e.you do Bachelor degree in Fashion Designing which is offered by many institutes in India. National Institute of Fashion Technology, Amity Institute of Fashion Designing and a few more. After 12th, try to get in those.

PCB would be sufficient, you do not need mathematics.

No stream is short of career. Let him choose what he is interested in.

You can do your 12th from NIOS board. They don't need any 11th certificate for it, just your 10th marksheet, Aadhar card copy, school leaving certificate and 2-4 passport size photographs.

MIT is Massachusetts Institute of Technology. The Massachusetts Institute of Technology (MIT) is a private research University in Cambridge, Massachusetts. It was founded in 1861 in response to the increasing industrialization of the United States, MIT adopted a European polytechnic university model and stressed laboratory instruction in applied Science and engineering.
You can check the below mentioned link for admission procedure:
http://googleweblight.com/?lite_url=http://mitadmissions.org/apply/international/howto&ei=rlySD4TQ&lc=en-IN&s=1&m=923&host=www.google.co.in&ts=1475920235&sig=AF9NedlZAfVZd9wIu1-jFtQASWsVF9u4Q

Hi,
To get admission for a Bachelor degree programs in any university, your class 11th and 12th marks are required. Your marks are decent, so don't worry.

You need to complete the minimum qualification i.e. HSC education for a better career. After that, you can opt for a regular course or vocational course. Anyway after failing in class 11th you can pursue ITI or a Diploma course. Kindly let me know about the stream in which you are interested.

There are various things that you can do. First is prepare by yourself. Rather than joining a coaching institute, make a study plan and work hard. But, you must be highly self motivated to ensure success. Second way to prepare is by joining a reputed coaching class. Whatever you do, you must remember that you will have to score will in your board exam as well.