I haven't had the test yet but I've heard plenty of experiences on here of people having 1:24 or 1:12, so frankly if I get 1 in 3000 odd I'll be over the moon! As you say, 0.28% is incredibly low, I'd try and take comfort in that. No one will ever get a completely 0% chance back, but yours is pretty close! X
Those are excellent results. my advice would be not to worry about it. Concentrate on your 20 week scan and assuming everything is as it should be put it out of your mind. If you are prone to anxiety and think it could cast a shadow over your pregnancy you could pay to have a Harmony test done and those results are pretty bombproof.