Light is important, lots of other things have been mentioned, but in my experience this plant tends to be a bit droopy. The main stem may grow sideways for a while, at least until it is surrounded by branches that lift it up, and eventually it becomes a clump. So this is not necessarily a sign of anything particularly wrong at this point, but there's also nothing wrong with reexamining how you are treating the plant.
Compare to this plant in a 3 gallon pot (maybe not the same as yours, but it's in the ballpark).
