Sandy, they wouldn't release a full Life is Strange game for free.
As Ana said, it was only supposed to be a short demo. I thought it was nice of them to release this "bonus" episode for free, and I they did a really good job with it, even though it was shorter than I was hoping it would be. I'm hoping that the actual LIS 2 episodes are quite a bit longer.
I'm not sure if you experienced what I did, but my playthrough ended prematurely when I triggered a certain interaction. If you didn't finish doing/exploring everything you wanted to, you can go back into the game, hit "Continue," and the game will start right before you triggered the interaction. Then, you can continue to explore as long as you want to. The game won't end unless you perform that exact same action again, so you can explore at your leisure until you've seen and done everything you wanted to. Then, when you feel that your playthrough is complete, you can trigger that interaction again.