Close your eyes and count your breaths. Inhale - 1, Exhale - 2, 3, 4.
Put your mind entirely on that and you'll calm down.
Also, don't jump right in (so to speak lol) See if she'll start you off as an old-fashioned. If you think of the orgasm cycle as a 100 meter sprint, men quickly peak at about 10 meters, then plummet down to the bottom and gradually rise back up and cross the finish line at 100. The key is to get over the 10-meter-hump without losing it. Then you'll be set for at least like 2 more minutes.