Hello Aspirant ,

If you fail in three subjects in class 12 you will have to repeat the class 12  again,  and you will be able to attempt the exam next year only , so i woulg suggest you to prepare well next year , attempt all the previous year questions you can , make your own notes and study daily .

You are only allowed to give re examination if you fail in only one subject since you failed in 3 subjects you can not give re examination .

Hope this helps.