How long will it take for me to perfect my serbian??

Okay.... So my parents came from the old country (Serbia), and when i was little i always spoke in the house, and now we hardly ever do, (Unless they are yelling at me, or talking about someone). I still speak serbian, and understand everything. I consider myself an advanced conversational speaker. My grandmother doesn't speak english, so all i do is speak serbian with her. Plus most of my friends are serbian, so i speak serbian with there parents. I am very active in the serbian community and speak the language a lot with the elders. Now, my parents are deciding to send me to srbija alone to stay with my family next summer, and idon't want to be embarred. I would say i know 75% of serbian. I just want to make it perfect. Don't think it would be that hard,considering i speak already. I just need help perfecting the accent, and learning the grammatical parts of the language, and of course learn more words lol. So i have a year, is that enough time to perfect my serbian? Also is there anything i could buy or do to help me?? THANK YOU=]]