Are all of your fasteners installed and in the correct holes? The liner as photographed is going to offer a full-on water and debris catch. I removed my liners to inspect the inner well (2005 Ocean, no accidents) and found the lower face of the rocker panels filled with compacted fine dirt and leaf matter. Surface rust had started and required sanding, rust removal and protective epoxy POR15 treatment and Waxoyl spray..
Those liners are essential to rust protection but must be installed in a way to have them operate properly. Periodic removal and inspection is critical to controlling corrosion.