I assume when you say rubbing, you mean lightly pressing on your belly, not just lightly rubbing your belly in circles to say hello to baby. I have always done the same thing when I had period cramps or had my husband do it. I have had stomach issues on and off as well with pregnany and found lightly kneading it also helps to kind of move things around. I don't rub as hard as i used to for cramps or anything or let my husband do it anymore, but as others have said, the ultrasound tech actually pushes pretty hard when you have ultrasound, so I think you're probably fine.
man, ditto on the ultrasound tech!! they really dig in there!!
but OP, think about those parents with young kids who jump on them all day long, or have big dogs that like to play, or you tossing during the night, moving around all day.. I mean... I dont really understand your paranoia