I Lied to Her

Okay, so I messed up. Big time. My girlfriend, Sarah, she's amazing. Like, actually cares about people, always volunteering, the whole deal. And me? I'm… not. I pretend to be, though. When we first started dating, I told her I volunteered at the animal shelter every weekend. It was a total lie. I was just playing video games. Now it's been, like, six months, and I keep having to make up excuses. She even wants to come with me 'next time.' I feel so guilty. I don't want to hurt her, but I also don't want to admit I'm a liar. What do I even do? I'm such a screw-up.