CR, first can I assume you are using a hand pump? Remember that the ball of sugar has thin and thick spots and will cool at different rates so you'll want to keep the temperature of the ball as even as possible.There are a few things things you can do. One is to puff slowly with the bladder, also keep rotating it so that the weight of the ball gets to move around a little and gravity doesn't take over to any one side. Also you need to control the hot spots. You should be running your hand over the ball as it's growing to help even out the temperature and keep it growing evenly. If it's getting too cool in a thick spot, you can hold it close to the heat lamp. Conversly if it's getting too warm and thin in one spot you can roll that spot over the marble to drop the temp giving the rest a chance to catch up.
Hopefully that will help you a bit.