What's funny is, I noticed the same thing when I first got my phone. I was just a little more "forceful" with it, considering the 45 day return window (for silver BB rewardszone) only start Sunday. After the first time I put the battery cover on (after installing the battery), it seemed to become easier.
I'm actually somewhat glad about this because it makes me feel like it's more seamless being such a tight fit.
Love the G-Note series!