You are very astute to realize that your topic isn't narrow enough. That problem happens a lot to students. Instead of changing topics, you probably will do better to take the subject you started with and narrow it to a particular group of people or a situation. Here are some ideas of problem solution topics on insecurities:
How can schools help high school students overcome insecurities about learning?
How can a high school student overcome insecurities in social situations with the opposite sex?
How can high school students help a friend whose insecurities are limiting their life?