rnb,
Your rifle will NOT be underpowered! It will do anything you need done out to as far as you can accurately shoot it. Take some of that ammo you got with the gun and go out and practice with it. See how far you can reliably hit a deer sized target offhand every time. That is the distance you can shoot at STANDING deer.
I personally do not shoot at running deer myself, but some people have learned to hit them reliably. If you don't know how to do it or have not practiced with this gun by shooting moving targets, then it would be best not to try it on live deer in my opinion. Good luck on your deer hunt but practice first! I think you will be surprised how much power the gun reallty has.
Bob H.