how long has it been up? it can take a while for it to warm up.
I know in NY This time of year my soil is very cold, so even when I have the rare day in the 50s, the ground is still frozen..
so picture your tent like an empty cooler and the ground like a block of ice... the inside of your cooler will be, well, cool.
the higher day time temps and increasing intensity and duration of sunlight should warm the soil and once the soil temps increase it will radiate warmth at night rather than absorbing it and you should see it improve. it just takes a lot more energy to heat the soil than it does the air.
