Hello there, so glad you're enjoying the demo so far, thank you so much for your kind words!
Sorry to hear you lost so much progress, especially since the demo doesn't have a functioning skip feature! Saving can be done once the notebook becomes available. There's a little green save tab you can click on inside of there.
Honestly, I'm not sure why we didn't throw in a tutorial for that (it's a very common problem, and so easy to miss!), so that's definitely a priority for the full release. Hope you end up enjoying the rest!