i'd bet $100 you're either pre-winding (counter-rotating) too much, or trying to spin too early before enough of you is off the lip.
you'll get it tho
I agree. Watch that video on 360's, it really has pretty perfect technique for learning. If you learn the correct technique on small jumps(not hucking, and doing your setup carvings/turning correctly, leaving the lip of the jump correctly, etc), it will transfer over to larger jumps much better, even if you can already land 360's or 540's on small jumps. If you setup carve correctly as mentioned in that video and leave the jump by popping off of both feet on the proper edge(either toe side edge for BS spins, or heelside edge for FS spins), you should be able to spin without "hucking" or trying to use your upper body too much to force your lower body around.
As mentioned above if you straight line to the jump and simply try to "huck" the spin too much by pre-winding and using your upper body to spin, you'll not only be off balance going into the air, but chances are you won't complete the rotation, or will land off balance and fall even if you do. If you spin to early(you setup too early and get on your edge before the actual lip of the jump), you will lose a lot of speed, probably stop spinning as soon as you get into the air, and land on the knuckle as opposed to the landing.
Either way hopefully you can get it figured out and land your first 360. I got over the 360 hump fairly quickly, but landing 540's consistently, especially BS 540's, was difficult for me. Best of luck!