Entity Framework: Duplicate Records in Many-to-Many relationship

I have following entity framework code first code. The tables are created and data is inserted. However there are duplicate records in Club table.

My operations are:-

1. Create clubs using club creation app

2. Create persons using person app

How to avoid the duplicate entry?

    static void Main(string[] args)
    {
        Database.SetInitializer<NerdDinners>(new MyInitializer());

        CreateClubs();
        InsertPersons();

    }

    public static void CreateClubs()
    {

        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = new Club();
            club1.ClubName = "club1";

            Club club2 = new Club();
            club2.ClubName = "club2";

            Club club3 = new Club();
            club3.ClubName = "club3";

            db.Clubs.Add(club1);
            db.Clubs.Add(club2);
            db.Clubs.Add(club3);

            int recordsAffected = db.SaveChanges();


        }
    }

    public static Club GetClubs(string clubName)
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            //var query = db.Clubs.Where(p => p.ClubName == clubName);
            var query = db.Clubs.SingleOrDefault(p => p.ClubName == clubName);
            return query;
        }
    }

    public static void InsertPersons()
    {
        string connectionstring = "Data Source=.;Initial Catalog=NerdDinners;Integrated Security=True;Connect Timeout=30";
        using (var db = new NerdDinners(connectionstring))
        {

            Club club1 = GetClubs("club1");
            Club club2 = GetClubs("club2");
            Club club3 = GetClubs("club3");

            Person p1 = new Person();
            p1.PersonName = "Person1";

            Person p2 = new Person();
            p2.PersonName = "Person2";

            List<Club> clubsForPerson1 = new List<Club>();
            clubsForPerson1.Add(club1);
            clubsForPerson1.Add(club3);

            List<Club> clubsForPerson2 = new List<Club>();
            clubsForPerson2.Add(club2);
            clubsForPerson2.Add(club3);

            p1.Clubs = clubsForPerson1;
            p2.Clubs = clubsForPerson2;

            db.Persons.Add(p1);
            db.Persons.Add(p2);

            int recordsAffected = db.SaveChanges();


        }
    }

Domain

public class Person
{
    public int PersonId { get; set; }
    public string PersonName { get; set; }
    public virtual ICollection<Club> Clubs { get; set; }
}

public class Club
{
    public int ClubId { get; set; }
    public string ClubName { get; set; }
    public virtual ICollection<Person> Members { get; set; }
}

//System.Data.Entity.DbContext is from EntityFramework.dll
public class NerdDinners : System.Data.Entity.DbContext
{

    public NerdDinners(string connString): base(connString)
    { 

    }

    protected override void OnModelCreating(DbModelBuilder modelbuilder)
    {
         //Fluent API - Plural Removal
        modelbuilder.Conventions.Remove<PluralizingTableNameConvention>();
    }

    public DbSet<Person> Persons { get; set; }
    public DbSet<Club> Clubs { get; set; }

}