Help...is she still hungry?

my baby is 13 days old and she drinks 3 ounces no problem, but she shows all the signs of hunger after she finishes her three ounces (turns her head and sucks on her fingers). So, I tried to give her 4 ounces a couple of times but all times she projectile vomited the forumla up. She only does this when she takes 4 onces. I always burp after each ounce. I don`t know what to do...what do you think?