Storing breastmilk bottles for short term use?

elduroq9

Ive been exclusively pumping and bottle feeding so that I know exactly how many oz he's getting, and I'm feeding him 2 oz at a time. I'm wondering if after I pump and I go to fill a bottle to refrigerate, can I fill the bottle to more like say 4 oz, refrigerate, feed him 2 of those, then put the other 2 oz. in the refrigerator for the next feeding? Or is it bad to heat breastmilk more than once? I don't have many bottles to store milk up at a time, and im definitely feeling like I can be pumping more than I am..