... なくてはいけない means have to do ... when it is used after 行く (go) , it becomes 行かなくてはいけない . In speech, the ては in the above form often becomes ちゃ , so it becomes 行かなくちゃいけない. なる can be translated as becomes。 行かなくちゃいけない + なる　--> 行かなくちゃいけなくなる It literally means: I "becomes" (to be in a state that I) "have to do ...", which in this sentence you can translated it into I was asked to an interview ... The past tense of the above form is 行かなくちゃいけなくなった。 The final の is only a particle (for emphasis, maybe). So: なくてはいけない（なくちゃいけない）＋なる＋た＋の　==> なくちゃいけなくなったの For the second, this should be syntactically wrong. But you can hear this form in real speech. It means "if you do not leave a good first impression". I think you can treat it as 第一印象をよくしないとね. と here is an particle shows an assumption, and the latter part (the "then" part) is omitted. ね is a particle with no real meaning.