Hello nrujinzo,
can you try to run the application as administrator? That should resolve the issue.
(right-click the app and select 'Run as administrator')
You can try with a small image, for example this one, so that it does not take too long:
(It took me 7 seconds to remove the background with this parrot image on my PC, so you can right-click and download this image to test it. This way you don't have to wait longer than 1 minute when trying it out, before deciding that it does not work.)
You can also try to minimize the app while running the background removal (by clicking the icon in the in the task bar) in case the issue is GPU related:
Please let me know if that works.
To get a refund, you need to contact itch directly. You can read more on it here:
https://itch.io/t/129454/how-are-refunds-handled