How do I move on from a girl that I feel I shouldn't talk to any more?

I recommend sending her an email, text, etc. telling her the truth. Simply say that you feel it's for the best that we don't talk to each other anymore and I'm sorry for wasting your time. Don't compliment her because she may get confused about why you aren't talking to her anymore. Also, don't say "it's me that's the problem, not you." Way to cliche. My Advice, keep it simple. Also, good for you for actually responding to her and not just never talking again. Good luck!