I have bug Legacy of the Vaal

I need help with the legacy of the vaal quest.
I killed a boss that dropped a core, but I accidentally threw it in the place where I was supposed to use it and the stone disappeared and I can't drop it again from the boss and I'm blocked from moving on to the next ques.
Act 3 cruel
I am asking for help because I cannot proceed with the main quest and I am blocked from accessing the end game.