Once you are erect and what is left of the foreskin is retracted she isn't going to know.
And if she does know what a guys junk is supposed to look like then she has been sleeping around and you wouldn't want to do her anyway.
The doc does not have to hold your testicles to see how things work.
Next time you get a physical if you want the doc to grab your boys ask him why some do and some don't.