If you need a corner ribbon and don't have what you need or can't make the ones you have work, don't fret. Some photo editors and I think MSPaint as well will work with the following trick (as long as you don't place anything underneath):
Open your photo or paper in the editor followed by your ribbons. Place your ribbons on top as you want them (rotating etc), crop if needed and save. Note that some editors don't like png files so you might have to crop them down to get the nice white background that may appear, which may also make you lose your shadow, but it's worth a try.
FUTURE HOPE: I made a template when I created these. I am always wanting corner ribbons and don't ever have what I need, which is how these came about. More are to come. I am doing primarys next. Hint to those that also design - not enough corner ribbons (or vellums for that matter).