>>893462>30 seconds of suffering. Most hunters I know have had at least one experience where they had to track a wounded deer. Sometimes for hours on end.
Given the spine shot, your deer probably felt little to no pain, and you finished it off rapidly.
Don't feel bad. Pay respect to the animal by using as much of its body as practical and return what you don't use to nature.
If you want to make sure this doesn't happen again, practice with your rifle. Figure out the wind conditions and other factors that led to the spine shot and train yourself for better shot placement and compensation for wind/distance/nerves.
Good job anon. You harvested a deer and did it fairly well. Now enjoy the spoils and don't feel so bad.
Pic related - where I prefer to shoot them.