Tolano

I recently obtained my first girlfriend (dont laugh, lol). I have a problem however keeping it down when we are together. This isnt a problem when we are fooling around, but it is very embarrassing when she is sitting in my lap with a bunch of friends around. She doesnt say anything until we are alone, and she is never mad, but it really bothers me. Is there some trick or does it just take time? I try thinking about things that arent sexual, but that doesnt work. Thanks for being understanding.