it probably just doesn't have a firm base. and if you dont tie it down it wont lst itself, the main cola will still shoot up. But it is in the perfect position to train. You should tie it down to the side of the pot the plant is leaning towards and then tie a seperate string from the base of the stem to the opposite side of the pot to prevent it from getting uprooted.
also if you are going to train one plant you should train all 4 (which you definately should if thats all the space you have) so you create an even canopy.