Call her. Tell her you were horny, too, and you feel like an idiot for not doing anything about it. If it'll help, tell her you were concerned about "protection" and weren't prepared but that won't happen again and when can you see her again?
Oddly enough, there's no magic or trick or technique, per se... "just do it" is the best advice anyone ever got about these things. I don't think there's any doubt she's into you, so just go for it. It'll be weird and awkward and you'll undoubtedly have better experiences later, hopefully with the same girl. Be in the moment... enjoy the rush, it only happens once.
You're in the bunker off the green, but you can get up and down for par from where you are.
