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Legally, you are in the clear. According to Colorado statute §18-3-402 if the person is at least 15 years old but less than 17 years old and the actor is less than 10 years older, no crime has been committed.
As far as getting into the good graces of her parents, that is something you're going to have to work on diligently. I think you would do well to approach her mother as you described near the end of your question. You can be with her legally, but the other considerations, as in her parents' approval, are going to take more work.
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