It would appear from your pictures that you are not putting the ring on properly.
There are 2 ways to wear cock rings. The first fits around just the shaft of your penis (which is what you have tried). The other is places the ring around both the shaft and testicles.
In both ways, you put the ring on while the penis is limp. As you become erect, the blood flow out of the penis becomes restriced and the penis becomes engourged with blood and thus thicker and firmer than normal.
To place the ring on just the shaft, slide the ring down over a limp shaft and begin stimulation. Getting a ring on over both the shaft and testicles is a bit trickier. Place the ring next to the scrotum and pull some excess skin through the ring. Gentley press the ring against one of the testicles and the testicle will slip through the ring into the skin you have previously pulled through. Repeat this procedure for the other testicle. At this point you will have both testicles though the ring, sitting under the base of your shaft. Grasp the ring with one hand and using the other hand, press the head of the penis back, down and through the ring. Grasp the head of the penis and pull it completely through the ring. Take care with all of this and be gentle. You must complete this procedure without becoming erect or you will get stuck in an awkward arrangement. To get out the the ring, you must become limp and reverse the process.
If you want to use the shaft/testicles method, start with a ring that is bigger than necessary and practice getting in and out of the ring and work you way down to the proper size. I use large rubber o-rings. Always use a ring that is made of a material that you can cut away if you get stuck.
Hope this helps.