Try to also tick Hi-Res Screen (see attached).
The MACH3 screen 1024 was made for a 1024x768 (aspect ratio 5:4) and NOT for a wide screen like yours which has an aspect ratio of 16:9.
If you can get a 5:4 aspect ratio screen 1024x768 or a 1280x1024 screen, then a GCODE circle will be round and NOT oval in shape on the screen.
If you MUST use a wide screen, then look for custom SCREEN SETS that other people have made that support wide screens. Some are free, others very cheap and others a bit more expensive.
If the screen is still small, it could be because the settings of the NVIDIA, AMD, Intel driver control panels has not been optionally set to stretch displays that are not having 16:9 aspect ratio.