Our house stays at 75. So even day old chicks are at 75 if out from under the heater.
With the heat plate it is around 85. So i think your chicks are ok and were just laying under the lamp instead of the heater.
They need to have a cool area and a warm area.
I personally use heating plates mine have always done good under them. And they dont stay under it all day.
Do you have a picture of your brooder set up?