Hi RiyaR,
Silly mistakes are usually the result of reading too quickly and not taking enough notes. Doing lots of practice problems probably won't fix either of those issues, so you should take a step back and work on your "mechanics."
Go back to the questions that you got wrong but shouldn't have and ask yourself "what could I have written down to help me avoid that mistake?" Then redo the question, from scratch - go through all of the steps (on the pad) and put some energy into the details. With that type of mindset, you'll find that most questions are just a bunch of little steps, you'll take the notes automatically and the silly mistakes won't happen (because you're doing all of the necessary work to remove the possibility of a silly mistake occurring).
GMAT assassins aren't born, they're made,
Rich