Adding numbers on label when if-statement occurs

I am making an app on windows forms application and I am stuck at a certain point.

btw, I am a very beginner in programming.

I put my code here:

        if (random.Next(3) == schat)
        {
            using (Graphics graphics = pictureBox1.CreateGraphics())
            {
                graphics.DrawImage(Properties.Resources.Schat, ClientRectangle);
            }

            MessageBox.Show("Hoera je hebt extra geld gevonden", "zoektocht");
            lblTotaalGeld.Text = Convert.ToString(100);
            double totaalGeld = Convert.ToDouble(lblTotaalGeld.Text) / 100;
            lblTotaalGeld.Text = Convert.ToString("€" + lblTotaalGeld.Text);



            btnZoektocht.Enabled = false;
        }

What I am trying to create is when this "if" statements occurs the second time.. I want the extra 100 dollars added to the bank account. At the moment I only get 100 and nothing adds.

I hope I make sense

Thanks in advance