The Chestbuster

I don't know if Ridley Scott answered this question. In part 1 Alien when the Chestbuster came out from Kane, we saw it as a small worm kind of creature. Then next couple of hours when the crew are deciding how to catch it, only maybe a couple of hours passed maybe (2). Then the next time we see it, it is fully grown, now if so?. When Bret picks up the skin it is still small, if the Alien was fully grown the skin should have been much larger, Kane's size a least like it's host, but it wasn't, So my question is What did it look like before it was fully grown, and What did it look like once it shed that small skin.