getting an issue while inserting datetime into Sql Database

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Text;
using System.Windows.Forms;
using System.Globalization;
using System.Data.SqlClient;

namespace TestProject
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void Test()
        {
            CultureInfo SpecialCulture = new CultureInfo("nb-NO");
            string GDformat = "dd-MM-yyyy HH:mm:ss.fff";
            string GDstr = DateTime.Now.ToString(GDformat, SpecialCulture);
            DateTime GDDate = DateTime.ParseExact(GDstr, GDformat, SpecialCulture, DateTimeStyles.AllowWhiteSpaces);
            SqlConnection InsertConn = new SqlConnection("Data Source=SOLID\\PUREEYEDB1;Initial Catalog=DB1_PureEyez;Integrated Security=True");
            SqlCommand InsertCMD = new SqlCommand();
            InsertCMD.Connection = InsertConn;
            InsertCMD.CommandType = CommandType.Text;
            InsertCMD.CommandText = "insert into Test(TestDateTime)" + "values ('" + "@GDDate" + "') ";
            InsertCMD.Parameters.Add("@GDDate", SqlDbType.DateTime).Value = GDDate;
            InsertConn.Open();
            if (InsertCMD.ExecuteNonQuery() != 0)
            {
                MessageBox.Show("Succeded");
            }
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            Test();
        }
    }
}