fluxuating temperature

so ive recently stated an indoor grow in my closet(what would be a washer and dryer closet), and i cant for the life of me get a stable temperature. i have a small 5" fan bringing air in, an 18" fan blowing around the room, a small fan in the ceiling sucking air up, and an ac duct pushing cold air into the room. the light is a 600 watt. and the room dimensions are 7' x 4' x 4'. the walls are covered in foil until the roof. the thermometer is right next to one of the plants in a square paper contraption so its not getting direct light. the temperature has ranged from 66.9 f to 91.4 f. while i am around i can open the door or change the ac tempt to keep it at a relative heat, but when i go to sleep or leave i cant do that. i woke up this morning to 91.4 (bad i know). so thats why i am here, any suggestions? anything other variables i need to account for? the door to the room is not entirely sealed so air leaks out of it. why am i getting 20 degree differnce? out side temperature?

any ideas would be great, thank you

sounds like you need a new thermometer. Or the way your fans are setup there is not direct airflow...possibly the air is just getting stirred around? just guessing. but i would take all that foil off and replace it with panda film or Orca film cause metal absorbs heat. also get a bigger outtake fan, the intake fan doesnt matter as much especially if you have a bigger outtake fan. and if you have A/C why would heat be a problem? put your a/c on a temperature controller.
hope this help

You want to be sucking hot air out. Put a high velocity inline fan near the ceiling sucking air from the room out. Cut a hole twice the size of the exhaust on the bottom of the room. The negative pressure created from the exhaust will suck cooler air in through this hole. You don't need a fan here. This is called passive intake.

Don't pump ac in,actively pump hot air out and passively draw cool air in.