2004 Honda Accord

First, I am new to this group and hope someone can help me with my problem.

I am in the process of changing the water pump and timing belt. I purchased a kit from O'Reilly that includes pump, belt, tensioner and idler pully. I have disassembled everything and installed the new water pump.

I was in the process of installing the new belt starting from the crank and going counterclockwise. I had it in place and was tightening up the idler pully when something slipped (also a loud pop) and the belt came off the back cam pully. The back pully has turned clockwise 45 degrees. I stopped everything and am know asking for help. I have no idea if I have caused any damage and how I should make any corrections.

Any help is greatly appreciated. Richard