Whenever we add or update in IsolatedStorageSettings.Save Method , need to save before application exit. I made little changes in your code, may this will help you.
private List<ScheduledAction> getStorage()
{
if (!userSettings.Contains("notifications"))
{
userSettings.Add("notifications", new List<ScheduledAction>());
userSettings.Save();
}
return (List<ScheduledAction>)userSettings["notifications"];
}
private void saveStorage(List<ScheduledAction> list)
{
userSettings["notifications"] = list;
userSettings.Save();
}