A slightly light-hearted response, but to all those concerned about cumming twice, be aware that there are quite a few of us who are delighted just to manage it once.
I think the most sensible policy, stated by someone else here, is just to make the most of your time and enjoy it as much as possible, without focusing on the outcome.
Personally, I have an issue with a tight foreskin which badly affects my sensitivity during any kind of sex (it won't retract at all when erect and is just fixed there like a big extra condom - didn't even know it was unusual until quite recently), but my drive to have sex and be with a woman is as intense as ever.