Hi ewen201,
Please consider:
不是你的: it was translated as ‘it’s not your fault...”; the phrase means ‘(what) is not yours’
該放就放: 放 means let go. Instead of ‘You need to forget it...”, how about “You need to let go...”
As for '軟', I think the translation will read better if either ‘soft’ or ‘weak’ is used. It’s possible to include a footnote if you wish to tell the readers that there is another way to translate a word/phrase.
Other than those mentioned above, your translation is good. :)
This is a really rough translation >_> I'm not the best at Chinese, so if anyone has any comments/corrections, please feel free to point them out!