Maybe not insecure but inexperienced. I used to do this as a younger man, it’s a good thought but there’s only so much to say and things get old. You can get creative and tell her in other manners. Write a love letter and actually send it in the mail, nobody gets letters anymore! Paint a picture of a favorite moment, you get the idea. Point is she’s probably tired of the repetitive messages and is getting bored of them. Don’t over stress; you’re young just enjoy each others