Growing an Avocado from a Pit?

I have finally sprouted an avocado "tree" from the pit! Yay! Unfortunately, during the busy summer, it has grown over 6-7" and is about 12", still in the water (not in dirt). I have time to plant it now, but am wondering if I should cut it back now, before I plant it, or if I should just leave it!?

There is quite a root system and the plant is very healthy, so I do not want to kill it before I even get it in the dirt. If anyone has any knowledge of this, I would greatly appreciate the advice. Thank you!

By Jess