SendKeys GUI Bug

I've made this program in C#:

namespace Spammer
{
    public partial class Form1 : Form
    {
        int delay, y = 1;
        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)
        {
            delay = int.Parse(textBox2.Text);
            timer1.Interval = delay;
            timer1.Enabled = true;
        }

        private void button2_Click(object sender, EventArgs e)
        {
            timer1.Enabled = false;
        }

        private void timer1_Tick(object sender, EventArgs e)
        {
                String textt = textBox1.Text;
                SendKeys.SendWait(textt);
        }
    }
}

It works fine most of the time, and it can really send keys quickly.

But when I insert a delay of, for example, 10 MS, it's very hard to click the "Stop" button to stop it. The only way to stop the sending is to close the program and I don't want to do that.

Is there anyway I can send keys very quickly, like 5-10 MS, without it impairing my ability to press the buttons inside the program? I can't click while it's sending quickly...