There is a problem with this quiz. Making each country tied to a specific "In the EU" or "Not in the EU" comes to be problematic when you get a question wrong. If I select the wrong one, than I can't get the next one correct, which means I have to select another answer, which will also be incorrect, meaning that you can't get a better score on this quiz if you get a couple wrong. You already note this, but it still makes the quiz very unenjoyable. It would be much better to make this a multiple choice quiz.
Currently, this is the only way to implement this idea - even a multiple choice quiz doesn't compare because there would be no location aspect. If you get a couple wrong, you need to mentally track it so you know which ones to skip over (yeah I'd imagine it's unejoyable but there's no other way to do it).
Could you not just have a quiz where you get 27 guesses and each European country is an option to be clicked? If you guess wrong you lose a guess. Seems a lot better than having to track once you've gotten one wrong.