You really need to get over your fear of doctors. They are like mechanics, but the machine they know is not a car, it's the body. They are there to serve you, and make you healthy, not to cause you embarrassment. Believe me, they have seen scary and amazing things, every single day.
None of us can tell you if the other testicle is trapped inside your body, where it can turn cancerous.
There was a guy who posted in here, who had one testicle, and fathered five kids.
You have two, because one is a spare.