Dont titanic, most of us need some time to get used to a camera like this so I dont think its broken.
I dont know if its a good idea to try out just with the paper, the thickness without film is different, and maybe something slips; and btw, is the back set to 120 and not 220?
And what I understand, the crank on the back is just thought to load the back and set it to 1, so just do so, cock the shutter with crank on the body and after that you attach the back.
And check if the multi- exposure lever is really clicked in the right position.
Have fun^^