@fBoyle-- I don't think it's a good idea to trim a goatee while it's still growing. It's better to let it grow until it's the desired length and then do the trimming and fixing. It's enough to use some oil or moisturized to keep the goatee looking neat while it grows.
The reason for this is because not everyone can get a good goatee. Some of us are more inclined to get hair on some parts of our face and less on other parts. Letting the beard just grow will give you an idea of whether you will be able to sport a long goatee or not. Trimming it at this stage is unnecessary.