The blanket is likely keeping the heat from coming thru.blanket is between the pad and wire
Best to have nothing between the pad and the chicks.
Post pics of the assembly?
Pads/plates work by the chicks touching their back to the heated surface. Much different than a heat lamp.it's only 64° under the pad
https://www.backyardchickens.com/articles/pseudo-brooder-heater-plate.67729/