Hi Deepesh,

Sorry, but you can't give improvement examinations at such gaps. You are allowed to sit for improvement examinations just after the year you passed out.

You can try for going by IGNOU OPEN UNIVERSITY at this time

Unfortunately you cannot give improvement exam woth on eyear gap. 

CBSE improvements exam can be given in succeeding year only which means 2018 in yiur case. Right now you need to be happy with whatever you secured.