In my opinion, you have made the right decision by dropping the PITS Pilani EEE branch for IIT Madras Metallurgy. My cousin was forced to take IIT Madras Metallurgy by his mother. Initially, he was disappointed but his mother advised him to continue with the same enthusiasm he cleared JEE. Many students after getting admission relax and this opens opportunities for those who continue to slog even after admission.

Your ultimate goal should be to change your branch for which you will have to work hard. This can be done by staying among the top 5% of the batch with around 9 CGPA. You can switch to Mechanical and even to Electrical sometimes with a good CGPA. All you have to do is

• Focus on your subjects
• Do well in the tutorials
• Perform well on quiz 
• Ace your practicals 
• Score high in the Final semester exam

IIT Madras has a plethora of subjects to choose from in addition to a dual degree. You can change your branch provided your academic performance is at par with the requirements in the 3rd year. Some other highlights that might convince you further to choose IIT Madras are

• Creative clubs like C5 help in harnessing skills in your area of interest. These clubs have made amazing innovations and you can always learn so much by being a part of them.
• The unique Research Park which is the IIT Madras incubation center 
• Extracurricular activities such as Yoga, 5-star Gym, long-distance running, etc.
• The Institute operates under the leadership of highly learned alumni and so are most of the Deans.
• Air-conditioned Central library that is stacked with resources

All these are unique to IIT Madras and thus it’s a better option than BITS Pilani.