If there's a way to mis-identify anything, someone will do it
but in general, it's hard to make a mistake by popping a very young snake. Sometimes people make errors when they see two little reddish dots that slightly protrude. These are the openings for the musk glands and shouldn't be mistaken for hemipenes. They're very small, but the male's hemipenes can be everted quite a ways. The other mistake happens when somebody tries to pop an adolescent or older male. They think that just because a hemipenis doesn't pop out, that it's a female. As Don mentioned, this may not be the case.