Hi RaghavSingla,
Practice CAT scores are only as realistic as YOU make the process of taking the CAT. The more the 'CAT-taking event' deviates from what you'll face on Test Day, the more likely the score is to be inaccurate (and in most cases, that means "inflated").
Here are some details to consider: When you took each of your CATs...
1) Did you take the ENTIRE CAT (including the Essay and IR sections)?
2) Did you take it at home?
3) Did you take it at the same time of day as your Official GMAT?
4) Did you do ANYTHING during this CAT that you couldn't do on Test Day (pause the CAT, listen to music, etc.)?
5) Were you retaking a CAT that you had already taken? Had you seen any of the questions BEFORE?
All things being equal, scores in the 690+ range are all fantastic, so you likely have little to worry about. At your scoring level, the GMAT becomes really 'sensitive' to little mistakes though - if you make too many, then that ultra-high score simply becomes impossible to achieve.
GMAT assassins aren't born, they're made,
Rich