Re: I think I messed up!
Don't worry about it. They will be fine! The only thing that could possibly happen is some of the oils from the prefolds could get on the other diapers, but I really don't think that is much of a concern. You can wash them again if worried, but I wouldn't bother. The oils in the new prefolds are removed with regular washing, so nothing special is needed for your other diapers!
SAHM to DD