Big caveat that I can't pretend to be able to contribute any kind of expertise here, but my gut sense is that you should take what your advisor said to heart! Personally, if I were an admissions reader, I'd be open to viewing your academic background as a refreshing source of diversity (e.g., it might shape your stories' subject matter in an interesting way). If this does prove to be an issue, maybe you can join a writing group or extension course to get some workshop experience under your belt?
In any case, there's nothing you can really do about this now, so I hope you don't worry too much about it! Easier said than done, I know.