It is normal for there to be a space at the back (hinge) of your PlanetBox.  It is an intentional part of the design and allows the box to accommodate the Dipper(s).
The back of the PlanetBox does not need to be flush with the hinge.  The space can be a little more or a little less than what is shown in the photo below.  The variable amount of space will not affect the functioning of the lunchbox.
Our stainless steel items are warrantied for 5 years from date of purchase.  If you have any trouble with using your PlanetBox during that time frame, please contact us so that we can help you.