@Jessica1378 Suggestions:
Set minimum nights to 2.
Turn off Instant Book until you have more experience and understand how to vet renters. They will have to send you Booking Requests so you can message with them to get a "feel" for them ad their reasons for booking and ask them questions to set your mind at ease. Make sure to ascertain if they have thoroughly read your listing description, House Rules, and Max. number of guests.
Don't use Smart pricing or Price tips. Look at comparable accomodation in your area and price accordingly.
Reiterate House Rules when answering a booking Request or Inquiry.
Enlist the help of a friendly neighbor to call you if anything seems amiss.
Under House Rules and Other things to note, write "Only booked and paid-for guests are allowed on the property. No exceptions"
Jessica, this booking was actually a blessing in disguise. You had a situation you didn't anticipate or want, yet nothing bad happened and the guest, while she certainly was remiss in not reading the House Rules, was apologetic and honest about what had happened. So you got a wake-up call right off the bat as a host, without having your place trashed, the neighbors irate, or experiencing something that made you feel personally unsafe and now you are aware and are informing yourself as to how to prevent such things in the future. Happy hosting!