Home made incubator?

[Shamo Hybrid]

It won’t go above 39.5 degrees, and the eggs were laid on 4-5 days ago

Are you sure you can't adjust it past 39.5? You keep pressing 'up' but it stops at 39.5?! I just can't see a manufacturer limiting their heating to just 39.5 especially given the fact that these Chinese incubators are soo inaccurate and a lot of adjusting needs to be done......

 

[IncubatorWarehouse.com]

One thing to remember is that a premade incubator's heater wattage is really only suitable for the container it was made for. You just put a low wattage heater made to heat a small container on a large open spaced box. Another thing to keep in mind is that the incubator is pulling its reading from wherever the sensor is located which is in the lid, not down on the eggs. Maybe try a low watt lightbulb for some supplemental heat to hold a little closer to your set temp.