Welcome to HCM
We understand your concerns
I went through your problem description. I don't you have any condition to worry.
The ring around your penis, or what you are interpreting as ring, must be the purple or dark colored vein, or some discoloration.
Don't worry about it too much as you are sure that there is any pain, burning sensation or trouble with the condition. To make sure doubly, you can visit a dermatologist
Hope this clears your doubts. Available for further clarifications.