Schosche switchBACK

Need to pick up a screen protector and case for my iPod Touch 4th gen.  Didn’t want it get be beat up too much.  Have a small scratch on the back.  Picked up switchBACK by Schosche.  It comes it a screen protector, a back case which you and put one of two of the backs on it.  For some reason the back covers are not going on.  Not sure why but it seems like they are to small.  Not a big deal.  Just want to put the blue back on it.