英语短语not exactly 和not really 究竟怎么用啊?我总是分不清楚这两个短语.

I'm not exactly sure what to buy Gill for her birthday,although I do have something in mind.虽然我心里确实想过买什么,但我还确定不了为吉尔的生日买些什么.You're not exactly sylphlike,are you?' she said to her fat friend.｀你并不算苗条,对吧?＇她对她那胖胖的朋友说.We're not exactly on intimate terms,but we see each other fairly often.我们虽算不上关系密切,但还常见面.not really 事实上不是例句:I'm afraid that's not really possible.恐怕这确实不行.Oh,not really.