Rocket Challenge!

Last year we started doing rocket challenges with plastic bottles. A bunch of schools around the world has been competing in this, but last year I wasn't in Kereru, so I couldn't participate. But this year we are doing it again! Now that I am in Kereru I can participate. On Wednesday we launched a rocket belonging to Lincoln. When Lincoln shot his rocket off it shot straight up, It was spinning in a really cool way as well, It went so high I thought if it was a bit bigger it might not have came down for at least 5 minutes but I'm not sure. Here Is the video of Lincolns rocket, just so you know It might be a bit hard to see the actual rocket but It's still cool,

I actually helped Lincoln put the sand in the bottle and while I was helping I was kinda thinking that since it had sand in it it would be too heavy but instead it was just right! After we shot Lincolns rocket we shot it again, but the rocket broke a bit and it had a burn on the end. I have and Idea on how I'm gonna do mine and if it goes how I wan't it to be I'm going to be very happy. I found out that extending your bottle and putting just enough sand to fill at least 3 quarters of the bottle makes it go better, I think I might mix a tiny bit of water in the extended part of my bottle so that it mixes in with the sand. What kind of things should I do to my rocket so that it goes better?