Why dentist does such a large filling for a small hole?

on the side of my front teeth i had a small hole and the dentist did the white filling and when i touch it to feel it, i am panicked to see that the filling is so large that it covers beyond the holed area i had, is it that the dentist must have mistakenly broken a portion of the teeth, i have heard that in the case of white filling the hole drilled is very small, i am sacred because people say white fillings come out and if my filling comes out it will be as good as i dont have a front tooth