pddm,
Which mock tests were you taking?
Did you go through the wrong answers in those mock tests to find your weak-spots? Since you have the Manhattan SC guide, you must be having access to their mock tests. Try taking a
MGMAT mock test and see which verbal section you are falling out on. It may not be SC! Why I ask this is since you got a 6 in the AWA, your grammar must be pretty good

If its SC, try to understand what kind of questions you are making mistakes in (idioms, tenses, parallelism, etc).
If its not SC, get the OG and do the questions in RC and CR.
A quant score of 46 is not bad. There could be several reasons why it went low. It is possible that you were hovering around 49 when you made a few mistakes towards the end, thus bring down your score. Perhaps you could change your strategy in quant. What I follow is pretty simple - spend a fair amount of time for the 1st 10 and the last 10 quant questions. I don't worry much about the mid 17 questions, I don't have statistics to prove this, but I feel that even if your accuracy decreased in those 17 questions, you will be able to make up for it in the end.
I would certainly retake the GMAT if I were you because having a score of 680+ boosts one's confidence to apply to better schools. Don't you think that you deserve a better GMAT score and a better business school? Go for it, I say

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Thanks Jaidev for all the advise. I will try my best to follow it.
You have a fantastic GMAT score btw...Congrats on that!
I'm planning for a retake now, even though it means missing some of my school's deadlines.
Hoping for the best