I was unable to get an erection in front of a willing lady last week. how do i fix this so it doesn't happen again?

Don't worry: This happens to all of us men. Sometimes the timing or the chemistry just isn't right. If you want to please her, you have your hands, your mouth, and the rest of your body to use. Don't "spectator", and do what you can to make her happy; eventually you will get your physical satisfaction and the pleasure of making her happen may be even more satisfying to you.