You cannot use the playertool to cancel this quest. The tool is also named after the PC, rather than the Quest itself.
Talking to him repeats the same failure dialogue, but it is never cleared from your Journal and you can still reenter the QA. As a result, I believe it is impossible to actually give up the quest.
There was an issue when LOSING to close the quest but hopefully now it's fixed.
Also need to kill less in order to succeed and lowered creatures HP.