You have done everything right, your testosterone is higher, your body and attitude more dominant. She is giving good feedback and IOIs as a result things get more sexual. What you aren't expecting is in daygame or public environment and with a new girl to get a hard boner. What you do to prevent or dissimulate this?

This you should expect to happen someday and be prepared to deal with. Biologically is a good signal, but socially you don't want it so much