Lowe the thermostat to 65F-70F also you really should have a bigger fan becuase you want an exhuast fan that will exhuast all the hot air and replace with cool air 3 times every minute.You have a 540 cubic foot room so you need atleast 800cfm at the least but first see if you can turn the thermostat down to 65-70F and see where that gets you,if it ends up being to expensice just get a larger fan or a second fan of the same size and make.