YOU HAVE BEEN JERKING OFF THE WRONG WAY! It's true you are not supposed to jerk off and cum on your stomach. you are supposed to reach your arm around your body, and pull ur cock from behind you and work it that way. YOu know what, I can't explain it properly watch the instructional video:

Now you get it right? Aren't you glad i'm here to tell you how to jerk off. If you didn't have me you would still be doing it wrong. By the way, its a bonus if you can shoot a load on your own ass!