Welcome to the Forum. This sort of contact, sometimes referred to as "frottage" certainly did not put you at risk for common traditional STDs such as gonorrhea or chlamydia. This is because the parts of the body in the buttock/anal area which are infected by these organisms are deep within the anus, not in the area which you contacted. Without contact, you need not worry about transmission.
There is a theoretical risk of acquisition of diseases spread by direct contact such as syphilis or herpes but in the case of syphilis, the disease is VERY rare and you likely would have seen a lesion. As for herpes, the disease is more common but the risk of infection, IF she was infected (and you do not know that she was) is less than 1 in 1000. Thus the risk for both syphilis and herpes is very, very low as well but for different reasons.
My advice is to not worry. This sort of contact did not put you at risk for an STD,. there is no need for worry or for testing. EWH
Correct. I would not worry. EWH
I guess that considering the chances that I contracted herpes are less than 1 in 1000 (if she was infected or shedding in that area) and the very short exposure I had, my chances of contracting anything would be quite theoretical ?
Thank you again