I have started to throw some 360's on the smaller - medium sized jumps, i have the carving and spinning pretty much under control but struggle with the landing. Sometimes i get it sometimes i dont and just slide out, finding that im not stomping the landing and riding straight away. more often than not landing and then being off balance or carving either t/s or h/s.
How are you landing, flat base, toe edge, or heel elge? I find that it's easier to stop rotation and stay balanced if I land a bit on my toe edge. Flat base is ok if I got the spin just right, if I land heel heavy at all I'm probably going down.
The rotation doesn't matter much, if I land toeside I can be off 45deg either way and still ride it out. I think it's from leaning too far back on the takeoff, when I do that I come into the landing a bit off balance and ass first. Make sure you're popping evenly off both feet too.
Focus on spotting your landing as you come out of the spin.
You might even want to try opening up your shoulders to slow your rotation down.
When you hit the snow then look up to where you want to go.
Take all the other distractions out of the equation.
Hope this helps.
Want to learn how to do some of the toughest snowboard tricks? Check out this resource on How To Snowboard!