You don’t have to copy a scene out the notebook to be romantic. You only need to show how much you appreciate her. A love letter is my go to thing. Its simple and it shows a point. The only thing you have to say is how she makes you feel or how she is so special to you. There are many other things you could right about but these two are the simplest. Simple is good but if you really want to show off than just write how you truly feel and be honest. You have to make her feel like she is your center of attention and that you love her.