It should get bigger! As soon as it makes a leaf, you should know if that's what it is or not, that's what it looks like to me too, Dahlia. It's difficult to stake these if you wait until they are big, more likely to break than bend.
I'd go ahead and put a tomato cage or some other kind of stake when you plant it. You won't forget where it is, or that it's there. Tying the stem to something has always led to the heartbreak of a broken plant, I don't recommend that method. Tomato cages are fugly, but I don't see them once Dahlia makes a flower.
Even after moving here where they don't need to be dug and stored, they toppled when I left them 'naked.' We do get high winds from tropical storms and hurricane remnants, other locations might have better luck with unstaked plants.
