I also have a bernina and love this walking foot, attached pictures for you - mine is about 5 years old, came with 2 sole feet for walking foot - see copy of instruction pic.
I always put the fork over the needle clamp first, and then the shank (V cone shape)under the positioning cone, holding my right finger under the walking foot, once I can see it straighten up so the needle is then in the proper position, pull down the fastening lever with my left fingers, it takes a little practice - not easy to attach at first. I wonder if you have on the correct sole for quilting/adding your binding, or if that would make a difference?
I hope this helps, and you get it working. Awful when things like this happens and makes one frustrated and stressed out.
Best of Luck.