You are lucky it was not worse than that, this is a typical what not to do when feeding live.
Feeding live responsibly means NEVER leave a prey unattended with your animal let alone overnight, always removed if uneaten after 20 min.
If you cannot feed live responsibly please feed F/T
Now when it comes to your snake chances are there could be an abscess which in that case would need to be drained and anti-biotic prescribed so take your animal to a vet