Nothing is impossible to achieve so don't you worry about the subject and judge how hard or easy it is. Just go with your choice, find what you are most interested in and in which field I want to do job in future. Choose that subject and then finally you have goal, ambition and will power to achieve your aim so nothing will be hard for you then, I guarantee.

So your aim is to become aerospace engineer, and I guess that is your dream job. So to become an aerospace engineering a very few colleges are in India but they don't have good teaching technology and can't get your dream job. So you choose mechanical engineering and then apply for M.Tech in aerospace engineering in Germany (there is a program you can find easily on internet). Because Germany is the best place in world for aerospace engineering, you can learn and apply your skills & you have various growing opportunities there.