Is it normal to see the black border at the bottom of the screen? ???
Yes, it is. There are differences between NTSC and PAL Amiga models (200 vs. 256 lines on the screen). PAL Amiga model, normally leave unused bottom of the screen when NTSC compatible game running. But, if you don't like that 'NTSC game on the PAL Amiga' look, it is possible to configure size of the WinUAE window or full screen mode for the correct aspect ratio.