Two things could be responsible:

1. Just a bad day.
2. Test anxiety.

Don't get too worked up. Take a day or two off and start again, it will pay off. Their is no point thinking about what's gone. If your target is around 680-700 try knewton. They have a 50 point gurantee, so it will be 680 or free for you.

All the best.

1) I have ordered the MGMT series (all 8 books) Would they help me improve my score?
A-Well those are nice books but i dont think your basics are flawed , i think it because of test anxiety you lost the track.

2) I am applying to Duke Early Decision and their application is due on Sept 29th. If I tell them that I am taking the test on Oct 1st, will they mind?
A- They have a rolling admission You can forward your scores..

3) Is there anything else I can do to improve my score?
A- Dont stress yourself..It happens be strong and positive..

4) What went wrong? I thought GMAT prep indicated your score well!
A-As Akhil also said test anxiety can be very harmful, On the other side you dont need much work little bit of review and practice can be the key for you.

Also dont take stress, It all good mate....

Thanks Guys.
The whole test day was messed up

I was traveling the week before and my flight home the night before was 4 hrs late

I drove through Hurricane Irene (45 mins each way) to take the freaking test.

A stupid fire alarm went off during the test- try concentrating with white and red flights flashing and a woman on loud speaker yelling "PLEASE EVACUATE THE BUILDING NOW"

But growing up, my grand-dad taught me the value of focus and concentration. And none of the above should have mattered and i should have championed on. I feel like such a failure.

Ok i am going to drag my feet for two more day and then get back on the treadmill.

Sad to know my $109 dollars towards MGMT books wont be as useful.

Thanks again

I can understand....Its disheartening to lesser than your target score....Though i do value your score....

You have all options option.. You may want to retake or get on with this score....Its just a piece of info about you.....

So enjoy and start focusing with your options.....

Hey calcpa2012:

Sorry to hear about a frustrating test experience! You know, it sounds a lot more like a really bad day than anything related to how well you prepared. I love that you're not making excuses, but it certainly does sound like you were most likely exhausted and distracted at least somewhat so the good news is that 630 is your baseline on a bad day - you can expect to do significantly better!

In terms of where you go from here, I'd strongly suggest a few things:

1) Analyze your recent (and next couple of) practice tests to determine which mistakes you tend to make when you're either rushed for time or feeling test-day stress and pressure. At least a handful of the mistakes you made on test day were preventable just by being aware of them - if you know that "when I'm rushing I tend to select the number that finishes my calculation - I need to double-check the question stem to make sure that, for example, x=5 directly answers the question...they could be asking me to plug that back in to get y" - then you know that the most important 3 seconds per question you can spend is double checking your work. If you know that when you're distracted you don't pay enough attention to the specifics of a conclusion, that's something you can slow down to do, too.

2) Give yourself concrete ways to get back on track when you lose focus or feel the heat. One thing that students often struggle with is that they know dozens of formulas and facts, but they don't quite know what to do when they can't find one that fits. That anxiety carries over from problem to problem - so have plan. If you don't know what to do on an algebra or sequence problem, try plotting small numbers just to get a feel for the situation. If you can't figure out what to do on a geometry problem, start listing your known quantities to see if you find a synergy between them. I don't know if you've read the debrief (on the front page of this site) from my friend Jason about his 780 score, but he freaked out on question 1! And then remembered that he should try to plot numbers to establish patterns if he's lost, caught the pattern in a few seconds, and went on to dominate the test. But he'll readily admit that it started off rough... He had a plan for what to do when things went wrong, and that was a saving grace for him.

Like Prateek said, it's probably not a matter of your needing to "know more things", but you can improve a lot by finding ways to minimize your margin for error.