IMDb:

Incorrectly regarded as goofs: It is frequently claimed that upon returning to the Rebel base after destroying the Death Star, Luke exclaims "Carrie!" when he hears Leia (Carrie Fisher) call "Luke!". Extensive examination of both the original and special editions has failed to provide sufficient evidence to prove that what he says is anything more intelligible than a cry such as "Hey!" [If anyone can get an official and authenticated statement from either George Lucas or Mark Hamill we might finally be able to put this controversy to rest - Ed.]