You don't need to buy it again. Just install the itch app and log in to the app with your account. Then click on Library in the sidebar to the left. Here you should see the simulator with options to install it, or after it's been installed, to launch it. I'm sorry I can't quite remember what the app looks like before installing the sim.
Another option would be to temporarily disable the anti-virus before downloading and extracting the zip. Or maybe the anti-virus has a quarantine where the zip is moved, and it could be recovered from there? Sorry for the trouble, I hope this helps!