GetDriveGeometry() Gives Wrong Information

I'm writing a program that calls the DeviceIoControl API in order to use the GetDriveGeometry method.  However, when I obtain the information from GetDriveGeometry(), most of the information is incorrect.  It gives the correct number of cylinders, but everything else (bytes per sector, sectors per track, disk size, etc.) is wrong.  I am mainly concerned with the disk size, but the other properties would be nice to double check that all the information is correct.  Can anyone help me find what is going on here, and how to fix it?

[DllImport("Kernel32.dll", SetLastError = true)]
        static extern unsafe bool DeviceIoControl(IntPtr handle, EIOControlCode IoControlCode,
            IntPtr lpInBuffer, uint InBufferSize, DISK_GEOMETRY lpOutBuffer, uint nOutBufferSize,
            ref uint lpBytesReturned, IntPtr lpOverlapped);
 
unsafe static public bool GetDriveGeometry(DISK_GEOMETRY pdg)
            {
                uint junk = 51200; //DISCARD RESULTS
 
                if (handle.ToInt32() <= 0)
                    return false;
 
                byte[] buffer = new byte[512];
 
               bool result = DeviceIoControl(handle, EIOControlCode.DiskGetDriveGeometry, IntPtr.Zero, (uint)0,
                   pdg, (uint)buffer.Length, ref junk, IntPtr.Zero);
 
                if(Marshal.GetLastWin32Error() != 0)
                    Console.WriteLine("Geometry Error: " + Marshal.GetLastWin32Error());
 
                return result;
 
            }
 
        } 
 
    [StructLayout(LayoutKind.Sequential)]
    internal class DISK_GEOMETRY
    {
        public long cylinders;
        public uint tracksPerCylinder;
        public uint sectorsPerTrack;
        public uint bytesPerSector;
    }
 
Console.WriteLine("  Cylinders = {0}", pdg.cylinders);
                    Console.WriteLine("  Tracks per cylinder = {0}", pdg.tracksPerCylinder);
                    Console.WriteLine("  Sectors per track = {0}", pdg.sectorsPerTrack);
                    Console.WriteLine("  Bytes per sector = {0}", pdg.bytesPerSector);
 
                    diskSize = pdg.cylinders * pdg.tracksPerCylinder *
                    pdg.sectorsPerTrack * pdg.bytesPerSector;
                    Console.WriteLine("  Disk size = {0} (Bytes) = {1} (Mb)\n", diskSize,
                    diskSize / (1024 * 1024));

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