Didn't think I'd ever ask a question like this, but can somebody help?

It sounds like you care a lot about this girl, even if you don't think she is 'The One'. I see no reason why you shouldn't start a relationship. You never know, you could start to feel that she is your soul mate over time. But anyway, in my opinion, relationships are trial and error. Try not to expect fireworks and true love out of a first relationship.