Forgot My Friend's Birthday

I totally forgot my best friend Lily's birthday this year. I mean, it was right after finals week and everything was chaotic, but still, how could I miss something so important? I even had a card half-written in my notebook for weeks! Now every time I see her I want to make some excuse about why I just didn't get around to it. But really, it's one of those moments where you know there are no good excuses. I should've at least texted or called to remember it was coming up. It feels like a massive oversight and I'm stressing over what she'll think when we finally talk about it.