Affection

So my GF (16F) is apathetic and idk how to deal with that, or tell her in a way she understands I (17M) guess. She is important to me and I want her to know that, but sometimes she just seems distant. I’m a psychical person to and I like to she my affection for her when I’m in person. I need advice on how to handle this because she is important to me and I want her to know that, and maybe even show her love as well…