Don’t spend the next few months thinking about what your size will be that night, big trouble man. PE, but see the extra size gain as just extra size on top of what you need to do her right (which is true based on your stats).
Also, try to get laid as much as possible in the next few months. Sounds like you have an awesome night ahead of you (wish it was me! lol), a little experience will go a very long way. good luck
btw, you’re planning on getting into that 3-some a virgin?? You’re a brave soldier lol. I think I would need to make sure I’m cool with 1 on 1 before attempting something like that. But hey, you’ll have a losing-my-virginity story that you’ll be able to brag about the rest of your life!!!