Modifying Django UserCreationForm

I wanted to add more fields to the standard Django UserCreationForm so I went ahead and subclassed it inside of my app's forms.py file and ended up with this:

class CustomUserCreationForm(UserCreationForm):
    email = forms.EmailField(label = "Email")
    first_name = forms.CharField(label = "First name")
    last_name = forms.CharField(label = "Last name")

    class Meta:
        model = User
        fields = ("first_name", "last_name", "username",)

    def save(self, commit=True):
        user = super(CustomUserCreationForm, self).save(commit=False)
        user.first_name = first_name
        user.last_name = last_name
        user.email = self.cleaned_data["email"]
        if commit:
            user.save()
        return user

I then went ahead and created a custom ModelAdmin for my Users, which looks like this:

class CustomUserAdmin(UserAdmin):
    add_form = CustomUserCreationForm
    inlines = [ProfileInline,]


admin.site.unregister(User)
admin.site.register(User, CustomUserAdmin)
admin.site.register(Class, ClassAdmin)

No matter what I do, however, the new CustomUserCreationForm does not show up when I go into the Admin page and try to add a new user. Where am I screwing up?

EDIT: It seems that the form is not being displayed, but is being used. If I try to add a new user using just the username and password fields that the typical UserCreationForm has, I get an error, which promptly goes away when I remove the add_form line in my ModelAdmin. Why is it not displaying?

I also do not have any admin templates in my local app directory. Could this be the issue?