FM intake for newborn

Hi Mummies! I am FTM. My son is turning 3 weeks old. I fed him 60ml of FM as instructed on the FM can but for the past days after each feeding he doesnt seems full. I then increase to 80ml and he seems more relax after feeding. My concern is will i be overfeeding him? Should i continue to feed him with 80ml or stick to just 60ml?