The top suggestion for very beautiful is ωραιότατος, but I was then marked wrong for using that. I reported it as being that the hover hints are wrong and my answer should be accepted, is that correct?
It's the neuter absolute superlative form of "όμορφος" that means "very beautiful". It is not taught in the course, but we expected you to use "πολύ όμορφο" as the sentence says "very beautiful", not just "beautiful". ;)