Translation:Your hat is really pretty!
Sometimes Duolingo insists on "beautiful" for "漂亮", and here it gives an example with "pretty" as the translation. I do thing "pretty" is better here, but I wonder why someone on the team doesn't just go over every question with "漂亮", "pretty", "beautiful", etc. and implement some consistency, at least in what answers are accepted, if not which word is used in the default translations.
The problem with all of your tries from Duolingo's perpective may be that you're missing the word "really", which is often how "真" is translated in this context (it's usually associated with the English words "true", "genuine", "real", etc.), even though there's not much difference in English between "really pretty" and "very pretty".
As for "漂亮", I'll quote user Keith_APP from a discussion we had about the Chinese words for "pretty" and "beautiful":
There is no clear distinction between these terms and the interpretation may vary from person to person. In general, 美丽 and 漂亮 are interchangeable and close to pretty. It is less likely to use 漂亮 other than concerning the appearance only. So we may use 漂亮 on a dress, on someone's make-up, on someone's features, and on someone's appearance as a whole. We usually do not say a natural scenery is 漂亮, but 美 or 美丽, or just 好. 漂亮 is also less used on things considered beautiful based on a specific aesthetic standard, e.g. a wall paper pattern can be 漂亮 but a modern art painting would seldom be described as 漂亮.
美 or 美丽 are also very close. We usually use 1 character 美 rather than 美丽 for something more breathtaking and not approachable, or based on a specific aesthetic standard.
I think that can be reported, though personally I would translate your English as "你的帽子真美（丽）".
I know the distinction isn't clear, context and personal preference can play a role, and Duolingo itself is inconsistent, but as a general rule outside of clearly idiomatic contexts where a particular word is clearly preferred in one language or the other, I now stick to "漂亮" for "pretty", and at least consider whether "美丽" should be translated as "lovely" or "pretty" rather than "beautiful". "美", for its part, I would almost invariably translate as "beautiful".
That's my general understanding of the relative territories covered by those terms, based on discussions with native speakers such as the one I quote above.