How do about this to happene when you have with a new girl?

Hello, this question is kinda stupid but I;m curious, I'm 25yrs young and well I had several times with different girls but ALL OF THE TIME the first and even second time my pennis is shy. and even though I'm not nervous I could be sub-consciously. How can I avoid this embarrasing moments because I'm going to have tonight with a new girl and I don't wanna screw up. Any advices please