You are not good at math and physics. If chemistry is possible, you can consider changing to a chemistry major, such as organic, inorganic, analysis and materialization. You must have studied the basic courses of biology and four major chemists. Feel for yourself if you are interested.
You don't have any foundation to take an examination of economics, management and computer. Unless you are very interested, it is enough for you to read these professional books again, but you still have time to read them in your junior year.
By the way, I noticed that you are a junior, and there is still some time to go to the postgraduate entrance examination. You can find books of different majors to read. There must be some in your school library. Talk with students from other majors, and decide your major of interest as soon as possible.