Your 2.0.1 serial number should keep the beta working at
least through the end of this summer. It sounds like you were able
to get it working, though?
And yes, FB 2.x can't open FB 3 projects. The project file
format is not backwards compatible. So if you want the option to go
back to FB 2, be sure to back up all your project dotfiles before
importing the project into FB 3.