Oh sorry to hear! I'll have a look, you're the first person with this problem. Did you try a controller?

Edit

Maybe I know what happened! Some tutorials have multiple sheets. You must look at the bottom left of the panel, and if you see a 1/2 it means that you must read a second sheet before being able to close. To change sheet, you can use Q and E (previous and next). After reading all sheets, you can close the tutorial. Sorry, I'll try to make this more clear in the future!