Depends on the airlines terms and conditions and where you booked it (online or through agent). Online bookings normally have a tick box to say you agree to T&C before you can make the booking, there is a cooling off period too, which you should find out about. Did you pay the full amount or just a deposit? You will lose the depoist, or worse the full amount if you are due to go soon, depends on the type of ticket and ticket class. You should have received a copy of the Terms and Conditions by now and suggest you get a copy ASAP and read them.
If you have just decided you dont want to go, even an holiday insurance company wont cover you having a change of heart.
Maybe youll just have to say you're worth it and go!