Choosing a stream or rather a career is an essential decision and one cant falter here.
Moreover changing decisions is a sign of being unsure.
Since you have appeared for medical entrance exam and now opting for management, seems to be a bit dicey situation.
Since you are shifting from Science to a Commerce stream.
Please be sure of it and then go ahead with your decision.
Before I proceed, I would recommend, an [Aptitude tests], whereby you are sure of your potentials and then can make a confirmed choice and will be successful too.
As far as choosing [management stream][2