Your plant height will depend partly on the strain and partly on how much light and space you have. I've heard of cannabis trees growing outdoors. If you have a 4-footer right now, depending on the strain you might want to top it (cut off the cola to make it bushier) or you can tie it down at a 90 or 180 degree angle, which will put it in shock a little and cause another branch to become the cola.

Or you can increase the temp in your shower up to around 82-85, which will slow the growth down due to the heat.