no i know that, but y does he have a normal right arm, that never happens in rocket states

Again that's his left hand that's normal (white) not his right arm. And yes he DID have an arm without a rocket on it for a few moments. When he has to use his hand to pull the lever on the Fourze Driver for a Limit Break.

thats wat im sayin, its fine thay had the left hand, y the right

because these modules are all interchangeable, so they included the Rocket state with normal arms, and then the rockets on the side, even though Gentarou never exposed both of his arm in the movie, Bandai didn't ship him without forearms.