Hey Riny,
You surely got a lot of questions. First and foremost, architecture is the core branch that teaches you how to design buildings, while planning is the field where you are taught how to deal with designing cities. This, i am explaining it to you in the most layman terms.
Next, yes you can opt for B.planning, however, dont think it is a grade lesser course than architecture, both are important and good careers in their own way.
Talking about jobs, as long as there are buildings being built and cities being founded, there are jobs for architects and planners. However, in this field there is no such mechanism as placement system at work. If at the end of the course, you are talented for the architect, you shall be picked. About the pay, i can assure you that the initial years are a bit of a struggle but eventually it is a very well paid job.
Internal upgradations do take place in NIT bhopal which depends on vacancy, which are usually there for a lot many people do change their minds after joining the course.
And finally, relax, and enjoy the process. and of course, all the best for counselling.