Wow! I was a Speccy user back in the day and got my first start in programming on that machine. I downloaded the demo of this game when it came out and was pleasantly surprised when I revisited it again recently and saw that it had been released. The final version is very impressive and captures the essence of Atic Atac in a modern way with a fantastic art style and retro sound.
I have noticed one thing however that might be an easy fix - the game does not appear to be aware of so-called "ultrawide" desktops e.g. 2560x1080. If I select "full window" or "full screen" the aspect ratio goes out of whack as the horizontal dimension is greater than the game assumes, 2560 as opposed to 1920. I assume there is no 4x scaling option as it was assumed that this would be the same as full-screen (1920x1080) on most machines.
Adding a menu option for 4x scaling, i.e. 1920x1080 would be great, or perhaps a software check to test the available desktop size, and reformat accordingly.
Best regards and well done.