Hi coolrahine,
I'm sorry to hear that Test Day didn't go as well as planned. Your practice CAT scores clearly show that you're capable of scoring at a much higher level. When these types of big 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, listen to music, etc.)?
5) Did you ever take a CAT more than once?
GMAT assassins aren't born, they're made,
Rich