You could try contacting Airbnb and plead new host ignorance and beg to have them cancel it for you penalty-free. If it was an Instant Book, you get 3 free Instant Book cancellations per year.
At this point, unless you have already changed those settings, I would snooze the listing and make sure everything is set up the way you want it before making it live again. Also, I would suggest that you set a maximum stay of 2 weeks or less. As a new host, hosting in your home, you really don't want to get stuck with an objectionable guest for a long period of time.
And you might also want to turn off Instant Book until you get more experienced. If guests have to send you a booking request, you would have seen what the price they were given was, been able to explain that it was wrong, and not accepted the booking, rather than have to deal with cancelling it after the fact.
@Rosemary280