Called the scam and fraud branch of usps, all they said was call my bank to get the charge taken care of. I asked if I should be worried about my card/information and they said "not really".
Didn't really give me much confidence, but, whatever. Bank can't deal with the charge until it goes through, as it's currently pending. It aint like they got my social security number or anything, so whatever.
Went from stressed to annoyed, so it's better than nothing.
*edit*
Woke up to seeing the pending payment did not go through. I think everything is alright now maybe? Either way, something happened in my favor.