Let me say first that I approve of how much FBF you did in this cartoon. Well done. There are only two things that I would take a look at if I were you.
The first is the guy's walk as he enters the stage. It's very unnatural. I'd recommend taking a look at how somebody actually walks. Stand next to a treadmill for awhile or something and actually observe it. It'll make things look a bit less awkward if you're working from observation. There's also a pretty decent tutorial under the Flash Tutorial section that can probably help you out, although I've found that there's no substitution for the real thing. Same thing with the dancing. Their legs aren't moving. If they were off the ground and floating, I'd understand it and it would looks less strange, but because they're on the ground just circling one another without moving their legs it just looks strange. Have them skip and side step a bit, or maybe hovering up and down in the air, whichever you prefer.
Secondly is when the girl's dress changes color. It's a cool effect, yes, but I'd be even more impressed if she was moving at the time. Something like floating into the air a bit while holding onto the guy's hands. That'd be cool. Really it just looks unnatural for the two of them to stop completely while the effect is going on. I'm sure with a shape tween it wouldn't be all that difficult to achieve a similar effect. Maybe she should just look down and raise her arms in surprise as it happens. Just don't have the two of them stop completely, especially after having done so much FBF earlier in the animation. It just looks strange.
Otherwise, good job though. It's a bit short and unpolished, but it was intended as a demo and was done in a few hours, so I suppose that's forgivable. That being said, you have time to shine it up a bit, just remember that your deadlines for the project outside of NG don't affect when you can put the final product on NG. No harm in putting in a few hours extra work to give it that extra touch if you know what I mean.