If he continues to do so, he may be stressed out by the amount of space. You will also notice difficult feedings if this is true.
Some baby ball pythons get stressed out with too much space, even in a 20 gallon enclosure, and roaming is often a sign of stress.

Make sure his hides are tight and the cage is filled with lots of cramped decor to hide in. Don't worry about it too much for a couple weeks. If he still seems stressed and/or doesn't want to eat, you may need to divide the cage or get him a smaller enclosure. :]