There is one way to utilize the other mounting holes on your shelf if you are worried about the load. You could screw together a wood frame, mount it to the wall studs with heavy screws, and attach the shelf to it.
I have the older Target shelf, it has different frame with more support and six mounting points on the outer sides. In my old house I mounted it near a room corner where the studs were closer than 16" and used this method.
I have the older Target shelf, it has different frame with more support and six mounting points on the outer sides. In my old house I mounted it near a room corner where the studs were closer than 16" and used this method.