Make sure it's at one even level of thickness before flattening it further. Dust with more flour as necessary. Work fast but don't rush. Try to roll out the dough before it has a chance to warm up. The key is to ensure that the dough has had enough time to rest and chill.
Cool dough is easiest to roll out.
It will start to stick and become unworkable as it warms up. If this happens, get it back in the fridge for a few minutes before continuing. Extra-cold dough, however, is also difficult to roll. If the edges crack as you roll it, it could mean it's too cold. Let it warm up slightly before continuing.