Hi Deepti,
I'm sorry to hear that Test Day didn't go as well as planned. When these types of score drops occur, the two likely "causes" involve either something that was unrealistic during practice or something that was surprising (or not accounted for) on Test Day.
If you can answer a few questions, then we should be able to figure this out:
When you took your CATs:
1) Did you take the ENTIRE CAT (including the Essay and IR sections)?
2) Did you take them at home?
3) Did you take them at the same time of day as your Official GMAT?
4) Did you ever do ANYTHING during your CATs that you couldn't do on Test Day (pause the CAT, skip sections, take longer breaks, etc.)?
5) Did you ever take a CAT more than once?
Thankfully, the GMAT is a predictable, standardized Test, so you CAN train to score at a higher level. We just have to figure out the specifics of what went 'wrong' so that we can fix them.
GMAT assassins aren't born, they're made,
Rich