Tell her you will quit smoking cigarettes if she will let you kiss your boyfriend.
If she won't go for that, you will have to stop kissing him in front of the cameras. In Texas were making out in our boyfriends cars when we were your age, and our parents never knew about it. Perhaps those days are gone.
Is there some reason why you want to get caught?
Think about what your mother is worried about. If you don't know, ask her. If you can understand where she is coming from and put her mind at ease, it will make her feel better. Perhaps then she will relax and trust you more.