you probably shouldn't plan on taking it twice, study REALLY hard the first time around
dental schools see both scores (i.e. they know you took it twice), but usually sitting the test 2 times isn't too bad, but I still wouldn't rely on that because it is a pain
that said, I don't think Mid-June is too late, I think it takes 2 weeks to process, and your app takes 4 weeks or something and the cycle doesn't even open until June 3rd