Кодируйте эквивалентный + = присвоение на событие

То, что необходимо сделать, установлено свойство выравнивания progressbar для исправления. Тогда установите LayoutStyle StatusStrip к HorizontalStackWithOverflow.

    private void InitializeComponent()
    {
        this.statusStrip1 = new System.Windows.Forms.StatusStrip();
        this.toolStripStatusLabel1 = new System.Windows.Forms.ToolStripStatusLabel();
        this.toolStripProgressBar1 = new System.Windows.Forms.ToolStripProgressBar();
        this.statusStrip1.SuspendLayout();
        this.SuspendLayout();
        // 
        // statusStrip1
        // 
        this.statusStrip1.Items.AddRange(new System.Windows.Forms.ToolStripItem[] {
    this.toolStripStatusLabel1,
    this.toolStripProgressBar1});
        this.statusStrip1.LayoutStyle = System.Windows.Forms.ToolStripLayoutStyle.HorizontalStackWithOverflow;
        this.statusStrip1.Location = new System.Drawing.Point(0, 250);
        this.statusStrip1.Name = "statusStrip1";
        this.statusStrip1.Size = new System.Drawing.Size(467, 22);
        this.statusStrip1.TabIndex = 0;
        this.statusStrip1.Text = "statusStrip1";
        // 
        // toolStripStatusLabel1
        // 
        this.toolStripStatusLabel1.Name = "toolStripStatusLabel1";
        this.toolStripStatusLabel1.Size = new System.Drawing.Size(117, 17);
        this.toolStripStatusLabel1.Text = "toolStripStatusLabel1";
        // 
        // toolStripProgressBar1
        // 
        this.toolStripProgressBar1.Alignment = System.Windows.Forms.ToolStripItemAlignment.Right;
        this.toolStripProgressBar1.Name = "toolStripProgressBar1";
        this.toolStripProgressBar1.Size = new System.Drawing.Size(100, 16);

    }

    private System.Windows.Forms.StatusStrip statusStrip1;
    private System.Windows.Forms.ToolStripStatusLabel toolStripStatusLabel1;
    private System.Windows.Forms.ToolStripProgressBar toolStripProgressBar1;