I take it bath bombs are classed as a cosmetic? I know that there is a minimum of the information on the front label, but no maximum- if you look at a lot of shaving soaps they have all the information on the front label rather than having a second one on the back
The answer to whether or not you need two labels depends upon what you have put on your label to begin with.
Your label must have:
Name of product - what is it
Type or scent
Your full business name and address
List of ingredients
Cautions if your product can cause slippery tubs, keep out of the reach of children, and if it is shaped like a food product it is a good idea to state it is not edible.
If all this fits on your label you are fine, if not you would need another for more space.