Hello @Deborah251,
I'm not sure from the description if you realise that instant book is turned on for the listing or if you do realise it and the problem is something else. It's just that there are many reports here where the host didn't realise that instant book was turned on for their listing.
With instant book turned on people who meet the minimum requirements set by Airbnb can book without the host having to manually confirm the reservation.
With instant book you should still get a confirmation email when a guest books. You could log on and check your notifications to see that they are set as otherwise you might not receive such notifications.
Click on your profile photo and select "Account Settings". In the "Messages" box check the boxes for each type of notification that you wish to receive and then click on "Save" at the end of the page.
Steve.