Most other responses have already addressed how to efficiently study in a long run. Now let's focus on this two-week issue. Here are some tips I usually use near the end of the exam, hope they may be able to help you somewhat.
Immediately schedule a meeting with your instructor/teaching assistant: Talk to them and express your concerns of lack of an efficient study tactics. Show passion to understand the subject, just not too sure how. There are a few pluses of this meeting. First, you put a face to your name, and even very subconsciously, the instructor/teaching assistant may take that into account and give you very minor lenience when grading. Second, they may give you some concrete tips on how to prepare as well.
Ask for a copy of previous test questions: This kind of documents allows you to gauge the breadth and depth of the test questions and general style/format. You can also use the questions for practice, but do not study the past test papers as preparation, because most instructors do not reuse questions. On the contrary, you may allocate less effort to study topics that were heavily covered last year or so. Chance is they are not as likely to appear compared to other topics.
Be very familiar with the syllabus: Dig out the course's syllabus and highlight all learning objectives. Use them as your study guideline because instructors usually use these objectives to guide their exam design. For each objective, at least be able to:
- define the key terms in the objective
- locate the chapter/section in your text(s) that cover the very objective
- describe at least one example or experiment relevant to the objective
- mention at least one application/implication of the objective
- say two to three pros and cons of the concepts in the objective
Use these as your guide to determine if you can check that objective off. Do not study anything that is clearly not stated in the syllabus. Strive for broad and systematic understanding, avoid potential ivory tower because you cannot afford it for now. Those types of in-depth learning should not happen 2 weeks before the test.
Once you have all of the objectives laid out, spread them out along your calendar and stick to clearing them batch by batch every day. Save the last day studying nothing, instead, use that day to go over some question and answer schemes in the books and review previous exams if you have obtained a copy.
Read the summary of each chapter first, and then read the main text: Most texts tend to concentrate the contents in the later chapter summary. Read that first for an overall impression of the structure. And then, with the syllabus objectives at the side, skim the text and look for key sections. Read those section carefully, and start to integrate them into your syllabus objective checklist. Once you feel that you have got about 80% of it, move on to tackle the next objective.
Keep notes, preferably handwritten notes: Using the syllabus as your foundation, expand it into a more structured "summary" of your study. Use only this one tool, don't jump from gadget to gadget.
Scrutinize the exam instruction: Read carefully what you can bring and should bring. Some exams allow books and some allow notes. Some require students to bring a calculator and graphing tools, some don't. Get those all clarified. Also, clarify with your instructor/teaching assistant that if formulas are provided or not.
On buying books: My attitude to books is always: Don't buy if you can rent, don't rent if you can borrow, don't borrow if you can take. A stalk of books on each topic within a subject is a bit ridiculous. First, most of them will be outdated or have a new edition by the time you can read them; second, they become a discouraging eyesore that only makes you feel guilty; third, most of them probably contain overlapped contents. A book not read is a book not owned, you may as well just keep a few seminal ones, and sell/donate the rest to simplify your study life.
On reading books: See this discussion thread.
Good luck and come back to let us know how you did.