Hello,
It's all up to you that you have to fill the form for the improvement examination for all the subjects or for one subject only since you have got somewhat less percentage in class 12 so you can fill the improvement form for the all five subjects or you may go with the one subject only or for two subject that's all up to you first make the criteria like in which subject you have got the least marks then fill examination form for that examination first then the second least marks and in this manner.
thank you