Help, I cant complete a quest i want to complete.

I was doing a quest called "The Calydon Ruins".
i believe this is a working quest however while i was doign the quest my inventory was full so upon extraction of an item as part of the quest i could not receive the item but the quest continued on. now i have everything for the quest but cannot turn in the quest because i am missing one of the items to complete the quest and when i went back to try to get the item i could not get it because i was no onlger doing that part of the quest. i have the 2 other items in order to complete the quest but not the first. can someone help me with this please?