Don't stress out! Keep calm and firstly run through the main headings in the HSC syllabus, e.g. balance of payments. Read selectively on the topic and pick out the main points, for instance, the layout of the balance of payments- balance on goods and services, net primary income, net secondary income (forming the current account balance) and then the capital and financial account. Then I would recommend creating a brief summary sheet about 1-2 pages for each topic and use acronyms and selective highlighting to help with memorising key concepts.