Ninject insingletonscope creating multiple instances per request

Question

I'm learning Ninject and doing a trial (thur a web api project).

I wrote a controller, which will call a repository and update elements in a data source

I have a class which acts as a data source (to kee things simple)

    public class UserDb
{
    private readonly List<UserModel> _listUsers;

    public UserDb()
    {
        _listUsers = new List<UserModel>();
        _listUsers.Add(new UserModel { UserId = "A123", CreditRemaining = 10.00, LastModified = DateTimeOffset.Now });
        _listUsers.Add(new UserModel { UserId = "ABC1", CreditRemaining = 20.35, LastModified = DateTimeOffset.Now });
    }

    public List<UserModel> Users => _listUsers;
}

In my Ninjectwebcommon file I create dependencies in following way

            kernel.Bind<IUserCardDetailsRepository>().To<UserCardDetailsRepository>().InRequestScope();


        kernel.Bind<LockingObject>().ToSelf().InSingletonScope();
        kernel.Bind<UserDb>().ToSelf().InSingletonScope();

Now for every request I make to the controller, it creates a new instance of UserDb, instead of using the one already created.

I thought InSingletonScope creates it once and distributes it, so the state of the object persists? What am I missing?