Main arm in back with the smaller arms pointing forward. Some bimini tops will have a tag along one of the outside seams. It also goes in back (if it was assembled properly).
Did you assemble the top yourself? Dang that is a hard job. I consider myself a pretty handy guy when it comes to fixing things and putting things together. But my gosh, you would think a 6th grader wrote the directions. It took me probably an hour just to assemble the frame and fabric. The boat assembly was much easier.