Bad shots happen to everyone. IMHO black bears are not hard to kill. I hunt black bears every year. I have killed them with a 30-30, 270-winchester & 300-win. mag. I have never been impressed with there "will-to-live" toughness. They can bite back so they do deserve respect. Just have confidence in your weapon & put the bullet/broadhead in the vitals. The only thing left to do is take pictures, gut & pack.
Good Luck,
WK