Your bonus healing is pretty good for you level. Getting to 64 and lifebloom will change your healing drastically but until you get to it, the best way I found to do it as I leveled was this:
Throw a rejuv on the tank before he pulls. Emphasis on before. When he pulls the healing will count against him as aggro and not you. You have to do this before he shoots, face pulls, charges the mob.
By the point you should know how much your regrowths are typically healing for and you can go ahead and start casting one when the tank has taken about half that in damage. That way when it does hit 2 seconds later you're not overhealing and at that point he'll have the HoT from the regrowth and the HoT from the rejuv on him.
I did that pretty much exactly that way from the 30's in SM till the 60's in Hellfire and Zangar.
Just wait till lifebloom :P You'll throw a 3 stack and a rejuv on the tank and /dance 3/4's of the time.