Hello Aspirant!!

No,you have not mistaken by choosing IIT Guwahati EEE branch ahead of Instrumentation as EEE also have better scope in future.You can also aware of the fact that IIT Guwahati has also good nirf ranking and overall both are of nearly same level .At last your hard work matters as you are interested in EEE then you will perform better in it.As taking branch of no interest have no value.

Good luck!!