I think I did the same as you in different steps, but I honestly have no idea - not a big computer guy
So the problem for me was that whenever i wanted to open the osbot.jar it would unarchive the jar. Which results in emptying the .jar instead of running it.
Solution: 1) open finder and go to 'go' and then 'go to folder...' at the the bottom and paste; /System/Library/CoreServices/Jar Launcher.app
2) open finder, go to machintosh HD - system - library - CoreServices - Jar Launcher.app
Once you've found the Jar Launcher.app, you can use it to open the osbot.jar. After doing it once, your mac will continue to open the file with Jar Launcher.