Don't feel too bad. I trusted Isaac, didn't investigate him when an NP said he made the kill, and ignored aok saying that Isaac was acting really sketchy.
But yeah, the number of people at EC was about the same as the number of people at Random. It would have been highly improbable for one of you guys not to be mafia. Doing a huge trust circle where everyone tells each other their roles is just generally bad too. Mafia's limiting factor now is that they can only activate one set a trap charge per day.