GMAT Strategy

Hello guys,
I have been preparing for GMAT since some time now. I am following the 60 Day GMAT course. Lagging behind with the schedule though. However my main concern is that I have been using a countdown timer with 20 mins so that gives me 2 mins exactly for each question but the biggest problem is that when I am aware about the time, i somehow get more nervous and sometimes not able to solve the question,I can't think or mess up the calculation. When I dont time myself, i think I do take 20-30 mins to solve them but between 6/10 to 8/10 accuracy. I have no idea what I should do. I am not sure if this is a common problem. This is just for quant by the way. Hoping I'd get some great recommendations