Well, first off, Sibelius is a notation program, not a sequencer. If you've made sheet music for this, you should probably attempt to get some live players on this, as it would help it drastically. And since Sibelius only uses MIDI sounds, there's your 'poorly sequenced' aspect right there.
Arrangement-wise, there is still a good bit of repetition. Try adding an original section of your own, or doing something that adds some variety in.
Remember, you don't have to emulate the source verbaitum. I've had a couple of mixes do that and they fell flat. It's arranging, not orchestration.