If you want to give improvement exam u should try in first attempt or same year.
U already taken a year,  u need to write either Full Subjects or Fail Subject in Board.

Thanks,
Azim

No you cannot give. 

Improvemnt exam can only be given in succeeding year of passing 12th which in this case was 2018.

Hence you cannot appear for 2019 attempt in improvement exam. 

Incase you have any doubts feel free to ask us in detail