If you are using a reproduction lever, this is not uncommon. If this is the case and the opening at the bottom of the lever is very wide, put the lever in a vise first and use the vise to close it up a bit. If you then close it up too much to go over the shaft, you can open it up a little by wedging a screwdriver or chisel into the opening. Once you have the lever closed enough and over the shaft, do as suggested above and install & tighten the bolt without the lock washer to snug the lever prior to final tightening.