It's hard to give a one-fits-all answer but there's several things you can do. Generally that is a common problem that stems from the champion more-so than individual shortcomings with bad macro decisions, although they can both affect each other. Kha'Zix with his kit is designed to get early leads because of his strong early-game matchups to most junglers, he has one of the highest snowball potentials in the game, and with that it's also very easy to fall of and throw your lead because of the assassin playstyle. Usually you avoid throwing by pressing your lead by setting the enemy jungler behind and enabling at least 1 lane to snowball with you, of course you'll have games where you have to play to perfection to carry despite 4 feeding teammates. Usually the goal is to enable 1 lane to snowball and carry while you extend pressure elsewhere on the map and trade objectives with them, or by extending their lead with yours through their lane and pushing them into a gold deposit they can't recover from.(edited)
Another general idea when you're snowballing is to be oppressive, spend more time in the enemy jungle, spend more time placing and buying pinks to place in their jungle at their camps. You want to make the enemy jungler scared to even walk into his jungle because you'll be waiting there. You want to watch the enemy laners so they don't roam onto you while you're doing this and catch you out (assuming you're aren't ahead enough to kill them all). You want to be as annoying as possible and starve the jungler. You want to push down earlier towers and take control over that side of the map once you have, smother them with your lead and kill pressure, just don't get complacent with your lead. By that I mean be very patient with your leap, when you jump in on an easy kill, factor in their escapes, their summoners, their backup.
It seems like a fundamental and obvious but those are the things you need to improve on the most, not just as a jungler but a player in general. A strong foundation built on solid fundamentals are where you're going to be in a position to improve the fastest. You need to get into that mentality if you want to climb faster, and avoid blaming teammates as much as possible, you have the tools to carry yourself out as a Kha main becase 9/10 games you can carry regardless of bad teammates.

Those are a lot of general ideas mixed with some specifics but if someone was coaching you, and going over replays, or vods of another Kha player it would be easier to break it down but those are general rules. For 1 major thing to take away from not throwing leads, I'd say think of your leap as a different ability than you normally do. When you watch top Kha players they will hold onto it and only jump when they're certain they will get the reset or if it's free. Think of your bounties as giving the enemy a free baron if they shut you down, which they basically get in gold. Also don't follow plays if you know they're bad, this isn't ranked teams, it's actually worse for you to follow up with a bad play and risk your lead. If you know a play is too risky or bad, spam ping back, don't be afraid to spam ping stupid plays or teammates. Lastly try to tax intelligently, when to shove, when to catch waves under tower when your laner is backed, when to push when the enemy laner dies. Try to learn wave management (plenty of youtube videos teaching it) before you tax too much.