You will need to use the BitBlt function to display the current bitmap. To do this, include the function in a WM_RBUTTONUP case in your window procedure, as follows:
case WM_RBUTTONUP:
hdc = GetDC(hwnd);
BitBlt(hdc, LOWORD(lParam), HIWORD(lParam),
Bitmap.bmWidth, Bitmap.bmHeight,
hdcMemory, 0, 0, SRCCOPY);
ReleaseDC(hwnd, hdc);
break;