Hi neerabu,
When you noted the silly mistakes that you had made, did you think about WHY those mistakes actually occurred? Usually, the best way to keep a silly mistake from happening is to write everything down. For example, you might be able to tell me what 21x12 equals (by doing the math in your head), but if you make a silly mistake and come up with the wrong total, then EVERYTHING you do from that point on in the question will be incorrect. If you want to be SURE of what it equals, then you need to write down the calculation and do the math ON THE PAD.
Sometimes silly mistakes are "math" mistakes, sometimes they will occur because you missed a "detail" in the question or because you couldn't remember a formula that you needed to use. Re-doing questions helps you to improve your "mechanics" (HOW you go about answering questions), so plan on including that type of practice in your studies.
Another thing to consider is "your approach" to answering questions. It could be that you're attempting to solve problems in a manner that is too complex. Most GMAT questions can be solved in more than one way, so learning other approaches to solving questions could make them "easier" to solve and you'll be less likely to make silly mistakes.
GMAT assassins aren't born, they're made,
Rich