When she's singing along the music and looking at me at the same time on the dancefloor, what to do?

Let's say, there's a girl on the dancefloor, she's singing along the lyrics. I have no idea of the lyrics but pretend to sing along. When I do that, I admit I look so freaking awkward and I think she notices that as well. She looks away. What to do? Keep pretending that I'm having fun? Or don't sing along the lyrics and just stare into her eyes with serious face?