About this 3D model

A replacement part for a Renault Clio rear door - a plastic mount which the door handhold fixes on to. The offending broken part is also pictured. I originally intended to print a mesh within the larger hole for the screw to bite into. However, these thin walls did not come out at all, so I ended up sticking a plasterboard plug in instead! We shall see if this works. Any tips on printing thin walls much appreciated.