In my incubator 55% is way to high but others run theirs there an do good. You can candle your eggs to see how they are doing an adjust according to air cell size.
I think you should at least have it stable for 24 hours before adding eggs. An it will take 24 more hours after that before it...
You could try a smaller water bowl an move it closer to the fan to raise humidity. Or use a coke bottle an make a wick out of a strip of cloth. Tie a string to it so you can hang the wick from the top in to the water. Adjust the height to adjust the humidity.
Placement is key with hot water thermostats. It has about 5 degrees between the temp it comes on at an the one it goes off at. If the thermostat is far from the light the whole incubator has to go up an down those 5 degrees. If it is very close to the light only the small space by the light has...
If your thermostat is a hot water thermostat it needs to be real close to the light. Something like 2 inches away. If its something more sensitive it should work there.