Dear aspirant,

I'm glad that you wish to give the compartment exam for Class 12. The question format and chapters will be exactly the same as of the the original Board examination. You don't have to study any thing less nor anything more. Also, yes, the marks that you get in the compartment exam will be your final scores. If you score less than your previous board marks, still the compartment exam marks will be added, hence, downgrading your result. So only give the exam if you know you can score higher than the marks that you have recieved.

Hope this helps!

Good Luck!