You really don't have much time, so we really have to prioritize. You took a practice test; use this article to analyze the results:
http://www.manhattangmat.com/blog/index ... ice-tests/Use that to decide what you are and are not going to study (there's no way you can come close to studying everything in only 3 weeks - if you try, you'll just burn yourself out and not learn anything very well).
In general, here are some major things to consider:
1) Do you have any timing problems? (The analysis you do with the article will help you answer this question.) If so, you need to address this. It typically takes 4 to 6 weeks to really fix timing problems, but you'll have to do what you can in the time that you have.
http://www.manhattangmat.com/blog/index ... anagement/2) Do you have any major weaknesses in the following categories?
Number Properties: divisibility, primes, exponents, roots
Algebra: equations in general (basic, exponential, quadratic)
Fraction and Percent problems
General word problems that require you to translate (into equations, etc)
Sentence Correction: modifiers, parallelism, subject-verb agreement, verb tense
Critical Reasoning: Find the Assumption, strengthen, Weaken
Reading Comp: specific details and inference
If so, those are the priorities. Other things you can ignore.
3) What materials are you using? Have you already got your books / online resources? You need these types of resources in general:
a) practice CATs
b) official practice problems (official guides)
c) books that teach you how to get better at the various things you need to improve (NOT just practice problems)