C# - Adding An Event To A "specific" Google Calender With GData API?

I'm trying to add an event to a specific calendar in google calendar and I just don't find how. Here's my code :

CalendarService service = new CalendarService("MyTEst");
service.setUserCredentials("Username", "Password");
EventEntry entry = new EventEntry();
// Set the title and content of the entry.
entry.Title.Text = "title";
entry.Content.Content = "test";
// Set a location for the event.
Where eventLocation = new Where();
eventLocation.ValueString = "Location";
entry.Locations.Add(eventLocation);
When eventTime = new When(DateTime.now, DateTime.now.AddDays(2));
entry.Times.Add(eventTime);
Uri postUri = new Uri("http://www.google.com/calendar/feeds/default/private/full");
// Send the request and receive the response
AtomEntry insertedEntry = service.Insert(postUri, entry);

Edit

Maybe I should mention that this fonctionnability is only accessible for an administrator of a site which want to easly add rendez-vous and note to his google calendar so I automaticaly authenticated it with "hardcoded" value so I'm sure the username and password are ok.