I am concerned that the flap of skin about the size of a quarter on my upper back of thigh is some form of std. I get a HIV test yearly.?

I doubt STD or HIV. I'm having trouble understanding or visualizing this "flap of skin". But no STDs, including HIV, cause anything like this. But see a doctor if you remain concerned about it.
See a dermatologist! Your description does not sound like any std, but I would strongly recommend that you see your dermatologist, particularly if the skin flap is something new. If you are not always having safe (protected) sex, you should be getting screened for more conditions than HIV (for example, syphilis, gonorrhea, chlamydia, hpv). If you are not having risky sex, but constantly worrying, talk to your doc!