Skyrim problem- I'm stuck

Trying to complete the "under sarthaal" quest

For those who can't recall off hand, it is the escavation site you are asked to explore when you join the Mage college at winter hold

Anyway, recall that you are asked to find some magical items, and when you find an amulet, you are locked into a small area until you put the amulet on.

The wall from the amulet then starts glowing or some shite, and you hit it with a spell and break through. You then carry on with one of your teachers through to find some Mage dude

Anyway, before getting to the Mage dude at the end, I decides to backtrack through and get all the goodies I missed. I did so, but then the bars from the little area you first get trapped in when you remove the amulet from the walk are now up again, thus locking me out of the deeper dungeons.

Anyone know what I can do ?