Trismegistus I'm concerned that after so long in the cb, I'll cum too fast when we make love.
If this happens just keep on and continue to try to satisfy her with your hands and mouth. At your age you will get another erection in maybe 20 minutes and can now start again. This time you will last longer as it's your second time. If problems do occur learn to laugh it off together and keep doing what you can and things will work out. There's no script you have to follow, concentrate on mutual enjoyment.
I've heard of guys masturbating before they join their girl to make love. This slows them down. It's an alternative IF you have problems.