I have the slim armor case. The easiest way to put it on is to already have the 2 layers put together before you put the phone in it. Put the phone in, press all around the edges to snap it in to place. And it fits perfectly right out of the box. No break in period required. If yours doesnt seem right, then its not right. Return it.
One question though, what kind of screen protector are you using? Is it a thick one possibly blocking the case from fully snapping on?
I know for my wife's iphone she got a zagg screen protector but the case kept making it peel off. She took it to zagg and they told her she needed a case friendly screen protector which leaves some room around the edges for a case.
Maybe whichever protector you are using is not compatible?
I ordered white, so the color met my expectations.