Good evening, we're just on a mixture, he eats 120 ml, after 1.5 hours…

Good evening, we're just on a mixture, he eats 120 ml, after 1.5 hours he may want again, then in two hours again 90, 120 and so on all day he may often ask for it. It's written online that you need to feed with formula every 3.5 hours, but it's impossible for the child to say that, I'm afraid of damaging his stomach with frequent feedings, is there an obligation to this interval? I'm afraid of overfeeding.