It doesn't matter. There's no such thing as 'messing up' one's reading. Just read on and take in what Milton has to say. You don't have a good ear. but so what? in fact, maybe you've simply no sense of rhythm but again, so what? There's no entrance exam on pentameters you must pass before you're allowed to read a poem. Trying to hear what you can't will only lessen whatever reward you might get from it.