Feed on demand or schedule feedings??

My formula fed baby is ten days old today. I have been feeding him when he’s hungry, pretty much every 2 hours, usually 2 ounces but sometimes it’s every hour and a half, sometimes every 3, sometimes he’ll eat an ounce and a half sometimes 3 ounces, I really just feed him when he wants to be fed. Today his pediatrician told me we need to stretch his feedings and instead of 2 ounces every 2 hours. 3-4 ounces every 3 hours. I have been trying to stick with this all day, but it’s so hard when I can tell he’s hungry and I haven’t waited the full 3 hours😐😐😐😐. I could understand if he was older but he’s only ten days old! Shouldn’t I be feeding him when he’s hungry???