It's pretty much not used at all, and no it can't be used to mean what you want. Mostly because a mile isn't very long. You could say "I'm miles behind" to get your meaning.
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Further a mile is long enough, about 1.3kg so when used in the context you have stated it adds to the magnitude of how far ‘behind’ at something one is.
Also, it would be more commonly used thus; ‘I’m miles behind at/in...’