@Candice7 the first guest made an inquiry, not a reservation request, correct? If that's the case, no, you did nothing wrong. In this business it's up to you to decide which guests to accept. In my view, the first guest who is ready, willing and able to book gets the reservation.
It's vital, though, that you understand the difference between an inquiry and a reservation request and use the correct terminlology when asking for help with reservations. You probably already know this information, but it might be a good idea to review this help article:
https://community.airbnb.com/t5/Tips-Tricks/Reservation-Inquiry-or-Request-What-s-the-Difference-A-C...