For the first time

I’m probably going to have sex with my (kinda lol) girlfriend soon and it’s gonna be my first time ever being intimate with someone. I have sooooo many worries. It’s not her first time being intimate with someone but it is her first time being intimate with a woman. I’m a super insecure person, i’m scared about all kinds of things, but I’m here to ask…What advice do you have for someone’s first time? What do you wish you could tell yourself before your first time? Anything I can do to prepare?