Help with my Nikon camera; focus is blurry?

I recently purchased a Nikon D3100 camera, however one thing is bugging me.
It makes so many of my pictures blurry. I currently have it set on P and the quality on RAW, image size large, but sometimes when i take a single picture, the shutter stalls and it comes out blurry (when the damn shutter opens, that is… )
When i use the lense to zoom in, it goes completely blurry and the flash is making things worse. Sometimes it works beautifully, other times, I want my money back.
I dunno… am i just a dumbass and am missing something completely obvious? or should i take it back to the store?

PS i have a sample pick of me and friend on her roof at night.we took this pic several times over and it got blurrier and blurrier each time- even with a flash.

Here's the pic:
http://s694.photobucket.com/albums/vv301/victoriatodd94/?action=view&current=DSC_0239.jpg
>>> Help with my Nikon camera; focus is blurry?