I'm sorry to hear that. It sounds a bit like something is going wrong with the food specialization menu that pops up when a creature matures. Does it look like this? (Maybe the buttons for some reason are not visible)
No worries! I'm glad all is well now. I'll see if I can make it more clear in the future. On that menu, you just click on a few food sources and then click ok, and everything should be good. I hope you enjoy the rest of the demo.