id repot that plat right away
when you dont have the soil all the way up to the top you not using your container effeciently and it could create airflow problems around the plant. also it will get your plant closer to your lights.
just let the soil dry out a bit..not too much...tip the container over and slide out the rootball...and refill the pot with enough fresh soil
to make the base of the plant even with the rim of the container.
also if you havent already started, its time to start giving that plant some nutes.