Hope you are well - sorry to hear about your GMAT disappointment. A solid understanding of Data Sufficiency is the key to GMAT Quant confidence. On test day DS can be really tough. Not because the questions get any tougher but because of that nagging bit of doubt: Did I miss something??? If you don't see your answer in problem solving then you know that you did something wrong but there is no safety net in Data Sufficiency. What to do? You need a solid strategy for the major DS questions types.
Make sure to understand:
1. When to pick numbers/make scenarios
2. What types of numbers to use
3. Counting equations/Unique Equations/Perfect Fit Equations
4. How to define a threshold
If you're a self-starter you can get this all figured out working through the OG 13
and using the GMAT forums as a teaching resource. There is ton of great information here. You might also pick up a DS book from Manhattan GMAT
or other fill in the blank company. I haven't used any of the books but maybe someone else can chime in. The other thing you could do if you don't have the time for more self-prep is to hire someone to help you. Provided that you're willing to put in the HW time it shouldn't take someone who knows what they are talking about to get you going in the right direction. Regardless of what resources you use remember that it's critical to keep and error log
so that you can learn from your mistakes. Make sure to review any doubts so that you have a solid strategy for everything. From 510-550 should be quite possible with a month of solid prep.
"It is a curious property of research activity that after the problem has been solved the solution seems obvious. This is true not only for those who have not previously been acquainted with the problem, but also for those who have worked over it for years." -Dr. Edwin Land
GMAT vs GRE Comparison
If you found my post useful KUDOS are much appreciated.
IMPROVE YOUR READING COMPREHENSION with the ECONOMIST READING COMPREHENSION CHALLENGE:
Here is the first set along with some strategies for approaching this work: http://gmatclub.com/forum/the-economist-reading-comprehension-challenge-151479.html