How to insert rows into Mysql database without duplicate?

When i want to insert a row into my MySql database 4 rows will be inserted instead of 1. Could you help me?

    MySqlConnection con = new MySqlConnection(cs);
                    string Query = "Insert Into csokolade (márka,ár,darab) values('" + this.Marka_Textbox.Text + "','" + this.Ar_Textbox.Text + "','" + this.Darab_Textbox.Text + "')";
                    MySqlCommand com = new MySqlCommand(Query, con);
                    com.ExecuteNonQuery();