Bro firstly if u have compartment than it's means you are less no in one subject and it's exam will be in may be in August than its my personal suggestions go for it.
Next thing improvement than its depend upon you how many subjects you will choose on next year i.e 1 or 2 or all subjects and improvement exam will be in next year 2019...
Bro last year i was also worried about this thing so may be my ans is right bz i know the cbse method may be
and sry for my engilsh...