Actually, Max Hunter, there's one thing they've never done in any of the episodes....
They've never said whether Pikachu was a boy or girl.
And they've always just said 'it' when referring to Pikachu.
So, I don't know how or where you got the idea that in that episode Ash said Pikachu was a boy, cause I know that never happened.
*has that episode on tape*
Anyway, here's some evidence for the fact that Pikachu's a girl:
1. Pikachu shows a lot of affection for Ash (just like Chikorita/Bayleef does), it likes staying on his shoulder, and it never wants to go inside its Pokeball, that sounds to me like Pikachu really loves Ash (also, at the end of the very first episode, Pikachu licked Ash, and in the 3rd season episode, "Chikorita's Big Upset", Chikorita even got jealous of Pikachu, cause Ash wanted to return Chikorita and use Pikachu instead, so Chikorita probably wouldn't have gotten jealous, if Pikachu was a male).
2. In the first season episode "Pikachu's Goodbye", Pikachu came back to Ash at the end, instead of staying with all those wild Pikachu, and if it was a male, it probably would have wanted to stay there (and this is also more evidence that Pikachu's in love with Ash).
3. Pikachu doesn't act like a male at all, and it definitely doesn't sound like one.
4. In one of the Master Quest episodes when they were at the Whirl Cup, Pikachu was in the audience and it was wearing a cute little pink jacket (or something like that).
And that's all I can think of for now, but I know there's a lot more evidence.