Help me.

Yes, Because there is a possibility of Elena bocoming a vampire, if she's killed in Klaus's ritual process because she has Damon's blood in her system. Dosen't necessarily mean she'd become a vampire but of course there's a huge possibility.
So if Elena does become one, then of course this is her last day as human. Stefan meant that he wanted her to enjoy her 'being human' for the last time I guess. Hope this answers your question.