I think you should read this a couple of times:
http://www.huntingnet.com/forum/tm.aspx?m=2987754
Then make sure you did everything listed in that post. If you haven't go back and see if you can't get back on the buck.
As far as the shot, if it was low and a little back you may have just passed through the brisket creatinga superficial wound that will not be fatal. If you caught lung that deer could go a long way before expiring, liver too.
Good luck.