See the images of several of the best paper-planes. Notice that their wings are slightly elevated, than a normal paper-plane. That is just what happens with me as well, a little elevation on the wings of a paper-plane makes it go faster and farther. Why does this happens?
Most paper planes are nose-heavy and for a very good reason. Basic aerodynamics tells us that putting the centre of gravity forward of the centre of lift, makes any plane (paper or not) more longitudinally stable.
The trade-off is that this configuration tends to cause a nosedive. The trailing-edge elevation counteracts this.
Note that, for the very same reason, all conventional-configuration self-stable aircraft are designed with negative tail-lift.
A not unheard-of cause of air accident for small commercial planes is pilots ignoring the loading specifications in order to please a customer. If the positioning of the load puts the C of G too far back, the plane becomes unstable. This may result in an unrecoverable spin.