الكود مش راضي يخزن بيانات بقاعدة البيانات

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

namespace ConnectionSample
{
  public partial class Form1 : Form
  {


  public Form1()
  {
  InitializeComponent();
  }

  private void btnAdd_Click(object sender, EventArgs e)
  {
  // declare and instantiate a new SQL Connection.
  SqlConnection Connection = new SqlConnection();
  Connection.ConnectionString =
  @"Data Source=.\SQLEXPRESS;AttachDbFilename=|DataDirectory|\NORTHWIND.MDF;Integrated Security=True;Connect Timeout=30;User Instance=True";
  Connection.Open();


  string sql1 = @"INSERT INTO General_Courses (CourseID,CategoryName,Title) VALUES

(@CourseID,@CategoryName,@Title)";



  SqlCommand com = new SqlCommand(sql1, Connection);
  com.Parameters.AddWithValue("CourseID", txtCourseID.Text.Trim());

  com.Parameters.AddWithValue("CategoryName", txtCategory.Text.Trim());

  com.Parameters.AddWithValue("Title", txtTitle.Text.Trim());

  com.ExecuteNonQuery();
   
  com.Dispose();
  Connection.Close();

  MessageBox.Show("The new free course has saved");
   
  }

   
  }
}

using System;