Stinger, I might also suggest you book a 2hr appt for your first time. Unless you've played a lot with your backdoor, it's going to be, ah, a bit of adjustment! It's definitely NOT something you want to rush into - going back there not properly relaxed and lube just hurts - and not in a good way!!!
Make sure you tell whoever it is that you choose that its your first time, and that they know how to be soft and gentle. A provider might be better for this since you can spend some time getting comfortable and aroused with her doing the regular boy-girl sort of things until you are ready for the main attraction.
Let us know how it turns out plz!