How dangerous is a head CT scan?

Before you guys call me out on my carcinophobia, I am doing significantly better today than yesterday. I did have one head CT a little over 2 weeks ago though and I am slightly worried about the radiation exposure. I read somewhere that this procedure averages about 2 mSv, which is significantly less than the FDA max, but I'm wondering if this one scan carries a cancer risk? It's the only CT I've ever had, and I've only had a handful of X-rays of my teeth as far as other screenings are concerned. Is this significant?