Bought basic nest thermostat and we set the temp at 68 degrees but the ambient temperature reads 91

[Bobbieb51]

Installed the basic Nest thermostat.  Set the desired temp to 68 degrees.  On the display it shows 68 for set temp but reads the house ambient temperature at 91 degrees or higher. It is definitely not 90 degrees in our house.   Maybe 69 or 70.    Help