You might have bugged it. The two things I'd suggest you do are:
1.) Check to see if there's a console option to go to the next step of the quest. (This is the better of the two options.)
2.) Get the construction set out, check the quest, and put whatever has the quest continuing trigger back into the cave. (Probably take a while to find whatever it is.)
I would definitely see into the console command. I hope this helped.