自己生成的bitmap图像在显示时有一条杂色的线，怎么回事啊？

Question

private void testfrm_Shown(object sender, EventArgs e)
        {
            unsafe
            {
                int* fib = stackalloc int[320*300+1];
                int* p = fib;
                for (int i = 0; i < 320*300+1; i++)
                {
                    *p = 0x00ff0000;
                    p++;
                }
                Bitmap small = new Bitmap(320,300,1280,System.Drawing.Imaging.PixelFormat.Format32bppRgb,(IntPtr)fib);
                pictureBox1.Image = small;
            }
        }
代码如上，知道的请告诉小弟下