Are you referring to the bottom, exterior of the slide, which you can see when the slide is extended? If so, then my coach had exactly that problem when new. It was caused by one of the teflon gliders being installed at an angle rather than precisely parallel to the bottom of the slide.
If there is no serious damage to the bottom of the slide, then the repair can be very simple by re-installing the teflon glider correctly. OR, if the bottom of the slide has to be replaced, then the repair is very expensive - the slide has to be removed and the exterior bottom of the slide has to be replaced.
You can examine the teflon glider positioning by lifting up the vertical carpet covering on the interior of the slide near the bottom. There should be holes behind the carpet that allow you to inspect the gliders.