I'm not big on tuning, but the most notable thing to me as a listener is that the voices sound muffled compared to the instrumental. Obviously volume in mixing has a bit to do with it, but you should experiment with flags and see how the sound compares to the instrumental so you can match it a bit. The second most notable thing to me is that the tempo sounds off, so if you give this specific cover a second try I recommend having the original song as a guide in a separate track and even play just the UTAU vocals over the original song (with the original vocals on, not just the instrumental) to match it as close as possible and even try to imitate the mix. The hardest part of UTAU covers in my opinion is matching the level of polish that the instrumentals tend to have, so best wishes to you!