1. Open your browser.
2. Type in www.[yourdomain].com. After it loads, does the web address stay on www.[yourdomain].com?
3. Then, type in [yourdomain].com. After it loads, does the web address “resolve” to the same address as it did when you completed step 2?
If not, your site technically has two versions of itself, therefore leaving search engines to believe that your entire site consists of duplicate content. This problem is actually very common, but fixing it is the one thing you should do right now to help your SEO.