I ignorantly did a quest to get me into the thieves guild. and there bad people. i want to kill them! i dont wanna work for them but i cant cancell. and i know there is a quest to take them out

You can't cancel quests are far as I know, but you might be able to get kicked out of the TG. I know in Oblivion, if you killed a Thief Guild member it was automatic expulsion.

I have that quest sitting in my journal and its annoying that I can't just delete it as I am not doing the thieves guild this playthrough.