That is very low humidity. You want it at least 30-35, some people even run it as high as 45. It will not go up when you add the eggs. You need to take a vent plug out, you need air exchange in the incubator. Did you calibrate your hygrometer?
In case you do not know, is not the volume of water in the incubator that raises the humidity, it is the surface area, so a large flat pan will give you more humidity than a deep small pan. I put sponges in my pans to help with humidity. Lockdown is the last 3 days and you want your humidity at about 60-65 at that point. I had to put in a larger pan at that point to get more surface area. I also ran tubing to the pans that stuck out of the incubator and filled the trays with a syringe during lockdown. I was using a homemade incubator.