DIAGNOSIS You likely didn't wait for the initial cooling period, or the interior thermal sensor is blocked. These small compressors need time to pull down the temperature.
FIX Set the temperature to the coldest setting (usually 34°F/1°C), close the door, and do not open it for at least 6-8 hours. Load it with room-temperature beverages, not warm ones, for this first cool-down.
IF THAT DIDN'T WORK Check for blocked airflow. The thermal sensor is usually a small plastic nub on the back wall. Make sure no cans or bottles are pressed directly against it, as this tricks the fridge into thinking it's colder than it is.
HEADS UP The exterior back and sides will get quite hot—that's the compressor and condenser releasing heat. This is normal operation. Worry only if the interior isn't cold after the 8-hour wait.