Hi Jaskirat,
The challenge you're facing is one I see all the time with clients. Despite the fact that the quant score differences are big between your attempts, the fact is we're really talking about 2 or 3 questions right / wrong making the difference.
That being said, what you're looking for is what I call 'shock absorbers' -- GMAT test taking skills that smooth out your performance despite the unexpected bumps along the way during different GMAT attempts.
Since you've been practice testing in the mid 600's, I'm pretty sure (but I'd have to test it) that your quant fundamentals are solid. My experience tells me your challenge is your test taking approach / process / strategies.
There are a lot of different elements:
1. Consistent process across all questions: capture, preprocessing, visualization, setups and execution are all key stages of every quant question. The first two are often when my clients were falling short before they experienced from performance coaching.
2. Timing / skipping strategy. Unless you're aiming for a mid 700's + score, you shouldn't be working on every question on the GMAT. And you need to keep a pulse on the clock at all times -- you need to practice this so it's second nature to you that, for example, when there's 35 minutes left you should around Q 13 or 14. If you're not, then you need to make adjustments immediately.
3. Advanced skills / techniques: across all the quant areas there a few advanced methods for everything between weighted averages to shape geometry. DS has a critical set of strategies that you need to master to ensure you consistently execute them quickly and accurately and avoid traps in the statements.
I'm happy to offer you our free 90 minute diagnostic session which will do three things:
1) Ensure you understand the GMAT and exactly what you need to do to beat it. That primarily means understanding that it's a test of executive reasoning (not a typical math or English test).
2) Answer the WHY question. Your ESR (live test) and answer keys (practice tests / mocks) only answer the WHAT question (ie. what types, topics, format questions did you get wrong). Why you got those questions wrong is the key to planning your retake prep -- that means a focus on your process for each question. Did you fall short in capture the info in the prompt or preprocessing the information in DS statements? Did you fail to visualize the problem to get away from the 'word problem quicksand' trap? Were your equation setups accurate and did you execute the calculations in the fastest, most accurate way?
3) Identifying other in test issues like time management, stress, fatigue, confidence, distraction.
Those are all things that a GMAT performance coach can diagnose for you in a 90 minute FREE diagnostic session. There's no obligation and you'll get incredible insights (from 1100+ of past clients) that will create focus, energy and efficiency in your retake prep. You'll more clearly understand your path to your target score with a higher degree of certainty. With a short time frame, you need everything you do from now on to really count and have impact.
Let me know if you're interested.