I believe the Deacon already has, compare the birthed Deacon laying near the Engineer carcass as it's first born.
Then when it's looking around, it's grown considerably.
But it's just all it is.
It's no monster, just an unloved child lol.
But seriously, the fantasy it turns into a great humongous beast, I don't believe so.
I don't buy that's Ridley Scott or anyone else's intent,
going by the concept art and everything discussed concerning it.