When you say that you are interested in science and are confused what to take up, its completely justified given the fact that there are so many specializations these days. The competition too is increasing and everyone wants to be the best in their respective field. A lot many students go through the same dilemma. Nevertheless, this can be resolved.
Before you make a final career decision its important that you know what are the various careers under science.
After 12th science you can consider options like engineering,medical,paramedical,biotechnology,clinical research, biological science, physical sciences, maths, chemistry etc.
Its advisable that you log on to http://www.youngbuzz.com/careers/career-options for more information on the various careers in science. It will give you information on the career, its scope, prospectus, opportunities, remuneration and benefits.
It will help you get aware about the careers and also narrow down your options.
Also log on to http://www.youngbuzz.com/career-assessment/role-assessment-career-counselling This will give you information about the career test which will help you make an informed decision about your career considering your interest (likes/dislikes), aptitudes (your potential) and personality(your work-values).
This will surely help.