You say you took the shot because you feared he may walk right past you??
So what???........so he walks......there are plenty of deer out there.
What if the only shot he offered you was a Texas Heart Shot???......Would you have taken that one too just because it was the only one available??
If all you have is a head on shot............you have no shot. Sometimes the deer win......accept it and move on. Don't take stupid shots and then try to justify them.........there is no good reason to take the shot you did.
Hopefully you will find him and this will not be a total disaster.
Why people take shots they KNOW are bad is beyond me.