When a contract killer’s life is thrown into a tailspin by a mysterious woman and chaotic circumstances, he kills the wrong man. Now he has only a few hours to find out how his flawlessly calculated hit went wrong and fix it before the Mob can take it’s brutal revenge.

I think you have a good and compelling story here, but I feel like your logline is a bit too wordy. Try to narrow it down a bit. I don't think we need the mysterious woman, or the chaotic circumstances in there - it seems a bit too vague. The basic information we need is that he's a contract killer, he's killed the wrong person, and that he's now running for his life. I hope this helps!