First, I would also clean-up and repair the existing holes as much as I could. IF you are working with particle board the holes can make it quite weaker. So, sand them down, fill with wood dowels and wood glue, let it all dry and sand it (again) smooth. Also, consider replacing the 2x2(?) that you currently have with something like a 2x4. Then you could make a few extra screw holes and have more surface area for the construction adhesive.