If a visitor looks at your page, he or she can only recognize the theme if for instance they've seen it somewhere else or that the theme is more striking than the content, which I hope isn't the case for you.
Whenever we opt to using free themes, it is better to personalize it as much as we can, not only to make it look premium but to simply make your page the way you want it to be. For instance, you can easily modify the color, the tabs, the fonts, the position of your photo, the title bar, etc according to your liking. If you aren't familiar with the ways on how to do it, simply search the internet, as I'm sure there are a lot of tutorials out there.
I also don't understand why you're so worried about people recognizing your theme as free. We all resort to free stuff.