How can I fix the display text which is read from a file using C#

private void btnFile1_Click(object sender, EventArgs e)
        {
            OpenFileDialog openFile = new OpenFileDialog();
            string str = string.Empty;
            string chuoiNoi = string.Empty;
            string line = string.Empty;
            if(openFile.ShowDialog() == DialogResult.OK){
                str = openFile.FileName;
                try
                {
                    using (StreamReader sr = new StreamReader(str))
                    {
                        while((line = sr.ReadLine()) != null){
                            chuoiNoi = chuoiNoi + " " + line;
                        }
                        lbFileA.Text = chuoiNoi;
                    }
                }catch(Exception ex){
                    Console.Write("You have an error: ");
                    Console.Write(ex.Message);
                }
                
            }
        }