C Sharp Data Base Oluştururken "Implicit conversion from data" Hatası

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

namespace WindowsFormsApp1
{
    public partial class Form1 : Form
    {
        SqlConnection con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=C:\Users\eminb\OneDrive\Belgeler\testing.mdf;Integrated Security=True;Connect Timeout=30");
        public Form1()
        {
            InitializeComponent();
        }

        private void Button1_Click(object sender, EventArgs e)
        {
            con.Open();
            SqlCommand cmd = con.CreateCommand();
            cmd.CommandType = CommandType.Text;
            cmd.CommandText = "insert into table1 values('"+ textBox1.Text +"','"+ textBox2.Text +"''"+textBox3.Text+"')";
            cmd.ExecuteNonQuery();
            con.Close();


            MessageBox.Show("record inserted successfuly");
        }
    }
}