Gotta have breathing space. In fact, there's probably not enough room at the sides for the type of fridge it is. Most older top mount fridges breathe out the back rather than the bottom like the newer full sized ones. Your fridge may die a premature death as it is, and your replacements will be limited because of the enclosure size. It needs to be wider.

If you find the space is needed for ventilation, then perhaps a grill, fitted to the space, would look better.