What do you mean by that? If the trim is not fitting tightly to the ceiling, it's typically one of tho things. Either the can protrudes down too low (adjust it upwards), or the trim isn't seating properly. Often you can adjust the cheesy bales that hold it in place.

the light and trim is one piece it is a insert.

I agree with Ron. In my experience, the problem with trim not tight against the ceiling is typically due to the fact that the tabs on the part of the light housing that gets inserted into the can have gotten bent and you don't get the proper friction fit. This can happen if the light is inserted and then pulled back out: the tabs get a little wonky and the second time the tabs don't hold properly unless they are readjusted. You have to inspect very closely how this is supposed to fit together and readjust the tabs as necessary. Is this by any chance a retrofit LED fixture?