Quit only during the end of the year of beginning of the year.
From what I understand of the LEAPS system, attendance is taken
into consideration under Participation category.
So lets say for example, you are currently in NCC. You wanna join,
lets say, IT Club. The attendance will be counted every school term
and if your attendance is 100%, it'll be stated in your report that
Term 1: 100%, Term 2: 100%. The problem with switching in the
middle of the year is if you switch to IT Club in june, your
attendance for NCC will still be counted for term 3 and 4, which is
both 0%. Similarly, Your attendance for IT Club also includes term
1 and 2, which is also both 0%. Its really not worth it to waste
those CCA points for attendance.
Approach your CCA teacher and ask to quit. My teacher said a CCA is
what you join based on your interest or if you want to learn new
skills. People who have selected a CCA that suits them will
eventually feel that the CCA is like a second family. Just quit.
Ignore all your seniors, even if they taunt you or anything, cos
you'll live a miserable school life if you join a CCA you have no
interest in.
Good Luck 
