ANSWER:

If its only a few grains then you might as well finish off.

However if its more and you are already full then it is wrong to force one self to eat more than he needs. It is best to give the extra to a needy person or an animal but if there isn’t anyone to use it, it can be disposed off.

How should we deal regarding eating food, for example if there’s some units of rice left in a meal , should we eat it so that nothing is left or is it okay to leave it that way