No? This is an Early Access, not a demo and not a beta.
I don't know that much about programing but I think it would be pre-alpha build? BG3 isn't at the stage to have demo (snippit of finished product) nor is unlikely to be feature complete (beta).
As to what you can expect from EA check the store discription of the item you purchased.
“Leading up to release you can expect a plethora of incremental improvements and new features to be added to the game, as well as the inclusion of new classes and races. The 1.0 release will include the full game including Acts 2 and 3.”
As every early adopters we will get to play test the whole game once 1.0 drops. Hopefully, if needed, there will be extra polish added with console ports.