What you have is the correct shirr plate for Box Style 11. (VS or 27 version). All the other styles have a different shirr plate
It is normally tucked under the ruffler.
Also looks like you are missing the set screw for the foot that the hemmers attach to. It is what holds the hemmers to the foot, so it's a rather important part - and very often missing, as is the set nut for the quilt guide.
Edit: it looks like the screw you have with the guide is the correct set screw for the hemmer. The one for the seam guide has a larger screw head, a shoulder to hold down the guide and longer threads- just like what you will find on the other Singers. In the picture below, noticed how much larger the screw that goes in that spot is.
The hemmer foot normally sits free - and the end of the tucker clips into where you have it in the box. The quilting guide tucks under that part of the three prong guide, and you have to futz with it to get the box to close properly as it easily gets in the way of the ruffler.
Here is a picture from the manual for style 11. Notice that the hemmer foot is not shown in the box, but it is listed on the parts list. And you can see the shirr plate tucked under the ruffler.
http://needlebar.org/main/puzzles/style11/index.html