Yes, the total episodes Aa! Megami-sama season 1 is 27 episodes
Episodes 1-24 is the main episodes of the seasons
Episode 12.5 ~Aa! Megami to Koukan Nikki?~(which i guess is the extra episode you mentioned), is the recap episode in between episode 12 and 13
Episode 25 & 26 are the bonus OVA which comes with the DVD release.
20-Nov-2006