So, I kinda lied to my mom about my first kiss, and now she won't stop talking about it?

It's never to late to say that it was a lie. Just straight up tell her that you lied. Tell her that you've just really were getting fed up with all the teasing on how you've never kissed anyone. Tell her that you're really not worried about it, not kissing anyone yet. That you're looking for that special *special* guy. And tell her that you will tell her when you do have your first kiss as long as she keeps it quiet.