I do not know how it is on the C152 to close the door in the air, must the speed reduced ?
The POH says...
Accidental opening of a cabin door in flight due to improper closing does not constitute a need to land the airplane. The best procedure is to set up the plane in a trimmed condition at approximately 65 KIAS, momentarily shove the door outward slightly, and forcefully close the door.
Although the only time I've had it happen it was with an instructor in the RHS, and he just stuck his hand out the window and slammed it shut again, at normal cruise speed.