Undertale bought but only playable like the demo?

I bought undertale in the Nintendo eshop. For 15 euro and I'm sure that I got the right game. But after the fight against Toriel it goes back to where I last saved. What shoud that?

Maybe uninstall the demo and install the full version?

I never had a demo
I just read that it will only be as long as the tutorial if you call yourself frisk and that's what I called myself

I see. Then yes…