I was given a new treadmill yesterday - BRAND NEW.. It's a Proform ZT5. I was so excited about it until I finished reading the manual. Its for 300 lbs or less. I weigh 321. What would happen if I used it? I know I can lose the 21 lbs, but I don't want it to break in the mean time, but its also too hot for me to go outside to walk (which is why the person bought me the treadmill). What do you think?