Correcto. Adverbs are genderless. They modify verbs, however, you should be aware that many adverbs are formed from the singular feminine forms of adjectives. Por ejemplo ¡No hablas sinceramente! Juan trabaja rápidamente. No aprendo fácilmente.
mikebrill - undeadgoat is correct. But also remember that when "demasiado" funcitions as an adjective it does have gender. "demasiada comida." = Too much food. and "demasiados niños." = Too many children or boys."