Is it possible to get your tongue periced to far back?

Well it could happen but the tongue would need to be really hyper extended for this to happen. Generally most folks "chicken up" a bit when the piercing is about to be done and that's generally when the clamp is being applied and they tend to pull the tongue back a bit before it's actually clamped. Now chances are really good that if you think the piercing is too far back it could be because the swelling has gone down and you're noticing how long the initial barbell is (trust me it's long). Once a shorter barbell in put into the piercing it won't feel that far back, the barbell will center on the tongue a bit better and will be much more comfortable.