It seems you are almost always able to beat the game on the second part. You just have to reach a point where you are able to catch a few of 'you' at earlier parts (like at the beginning), then run back and catch the ones you just let by then while going for the earlier ones.
The demo really isn't the same as the actual game. Yes, you do levels like that, but its much more open to your decisions of where to go and what to get.
 "One Step Back"){kind=icon}
 "VVVVVV Demo"){kind=icon}
 "Learn to Fly"){kind=icon}
 "Pirate Defense"){kind=icon}
 "Smatch"){kind=icon}
 "Exploit"){kind=icon}