Hello,
Getting a job in Google or not does not depend on marks you secure in class XII. At the end it all comes down to the knowledge and skills you acquire.
Do not worry about your class XII result, prepare for engineering entrance exams. Getting a good college preferably IITs, NITs, IIITs would increase your chances of getting placed at Google.
Also, even if you did not get into a college where Google comes for placements, try to acquire relevant skills and apply through direct recruitment which are opened on the Google official website frequently.

Good luck