Becca, I got the Music Theory in Practice workbook when I was doing Grade 2, and although it's good for sample questions, it doesn't explain everything in detail. For Grade 2 I found the "First Steps" (ABRSM) book really good - it tells you everything you need to know for each grade up to G5.
Make sure you know the relevant scales, key signatures and time signatures above all else.
In the exam itself, make sure you don't make any silly mistakes which could cost you marks, like writing an ascending scale when it should be descending, for instance. Read the questions carefully, and check check check everything. Even if you finish the paper with half an hour to spare, re-read the questions and re-check your answers right up to the last minute. Or try and improve upon your rhythm composition.
Try and do your past papers under exam conditions and see how long it takes you.
You've still got a couple of weeks to go. Plenty of time! You only need to get 66 out of 100 to pass. If you have any problems, ask on here and somebody's bound to be able to help you

Good luck!