If your wondering why nicht seems to go all over the place, it is actually really consistent. After a quick google search, I found this website that does a decent job in explaining the concept of nicht: http://german.about.com/od/grammar/a/The-Position-Of-Nicht.htm
Aechos, "jacke" is feminine in German and that is why you have "deine" before it. (https://www.collinsdictionary.com/dictionary/german-english/jacke)
As far as the translation of the sentence goes, I think admin guys of Duolingo need to accept "the jacket is not yours" as a true utterance and translation as well, unless they reject it as incorrect for emphasis's sake, which can be tolerated.