If it says that it can't be opened, open Terminal, type cd, space, then drag the application into the terminal and enter. After that, go into the package and go into the MacOS folder. After that, you type chmod +x Contents/MacOS/(the name of the document/s in the MacOS folder). This will usually turn it from a document into an executable and it will work. If it doesn't change it, it might work but also might not. After this when trying to open it, try once by double clicking, then right click and click open, then open anyway.
Viewing post in Unable to start game on MacOS 'The application can't be opened.
The solution to that problem varies from game to game, as I have not purchased the game, I cannot give advice on this matter. For me, I usually just search around in the settings looking for a resolution or fullscreen setting and adjust that accordingly. If you can't see the edge of the game, it is likely that the resolution is set for a screen larger than yours. Some flash games that I played have a similar problem, but they were designed for smaller screens.
I would recommend attempting to contact the developer with issues of screen resolution and device compatibility, as they would likely have far more insight than I do.