When we say skin to skin, we really mean "direct unclothed skin to skin contact of the mucous membranes of the mouth, genitals and anus with friction".
The only way STDs are transmitted are oral, vaginal, or anal sex, and sometimes heavy grinding/rubbing can transmit certain ones.
HIV is only transmitted by unprotected vaginal or anal sex.
Hep C is ONLY transmitted by blood, and is very rarely sexually transmitted. When it is, it is almost always anal sex.
HPV is VERY common, and can be transmitted by rubbing and grinding, but nothing you did sounds like you'd be at risk.
You aren't at risk for any STD.