Definition of fortune is chance or luck as an arbitrary force affecting human affairs.
Since belief in divine decree is an article of faith. Is a Muslim doing kufr if he says "unfortunate"?
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The Prophet (peace be upon him) said regarding Islam: “This religion is one of ease and not restrictions; no one tries to make it strict or difficult, but will be overcome [him]; therefore do what is right, and do what you are capable of, and be happy, and seek help by performing prayers.” (Al-Bukhari, 39)
I have had the same thought. From what I found out, you don't necessarily become a Kufr by saying so. Having said that, there are certain uses of language that we must change to stay on the safe side.
How lucky/fortunate am I? This is phrase is used to express joy when we are blessed with something wonderful. The above phrase is very common in the English Language and comes very naturally to an English speaking person. As a believer, you should try to replace it with phrase, "Alhamdulillah"; meaning 'Praise be to Allah'.
Instead of the phrase, That's unlucky!; try saying: "That's sad. BarakaAllah (May Allah Bless you)".
I agree with the answer Nate has given. Do not try to make things hard for yourself. I hope these tips help you.