@Taylor4, I checked your listing, and noted that your House Rules are minimal. You need to be far more specific. List clearly the kinds of rules you want - and expect - guests to follow. This includes not bringing an additional guest into the house. The booking was for one person, not two. The rules should also include not having unauthorised visitors on the premises at any time.
I also noted that you have no Security Deposit in place. I'd recommend adding one.
I see you do have an 'extra guest' charge. Was this in place at the time the guest booked? If not, it's doubtful you can make a claim.
Perhaps you could try via the Resolution Center.
https://community.airbnb.com/t5/General-Hosting/The-Resolution-Center-A-Community-Help-Guide-Request...
If it were me, I'd put it down to experience and move on. But be sure to beef up your House Rules. Check other people's listings for private rooms to see what sorts of things are indicated. You can be sure that most of the rules are in place on the basis of a host's experience. 🙂