Hi Gazzarooni
Welcome to Poker Strategy Forums. You did really well for your first tournament. It's easy to get carried away when you are the chipleader because you usually have a dominating image and are playing power poker, raising with some marginal hands, etc. The key is knowing when to change gears and who to change gears against

After a while people just get fed up with the power poker and throw out the stop sign and make a stand, so you will need to have a hand to show them.
Regarding your Kings against jacks hand, I don't think the end result would have been any different. If you raise preflop the
BB with Jacks is most certainly going to call, and possible reraise anyhow getting all the chips in preflop. Even if he just flat called your raise, it is going to be near impossible for you to fold a j x x flop.
I like to call this being "a victim of circumstance". Almost nothing you could do to avoid the outcome.
One of the partners on this site has a great
Sit N Go site callled SitandGoPlanet.com. I'd highly recommend checking it out, there are a lot of poker strategy articles that are very specific to sit and go tournaments. Quite often the best play in tournaments is significantly different than what the correct play in a cash game would be.
Once again, welcome to PSF
Jason