in my opinion you have to comlete an exam paper using whole time because if you use to complete the exam as fast you can make many mistakes so you have to take whole time and prepare for your exams.
The best solution if you don't want to finish the full paper is to finish 3/4 of it, so that it is almost complete. If you get all the marks right on 3/4 this will get you at least a C and possibly a low level B-.
I don't understand you that much bro sorry...
But are you trying to say that if I completed it quickly I would lose marks?