well I started off just trying to do flat 3's to get the hang of it and then I moved onto like 4 or 5 foot high jumps
Ok, you took too big of a step. Here is the fool-proof way to learn b/s 360s.
(I assume everything for a regular footed rider)
Find a decent roll / knoll / etc. ("jump") on a green or blue trail. Ideally, this jump will be on the right side of the trail.
Before you get to the jump, carve over to the far left side of the trail.
Approach the jump so that your are riding perpendicular to the trail (toe side of body facing directly up hill, heel side facing directly down hill).
Hit the jump, from the side
, and spin a b/s 270. The result of this, since you hit the jump at such an extreme angle, is that you will land riding straight down the hill.
The idea is to cheat
the amount you have to spin. By taking an extreme start angle, you only have to spin 270 to ride away clean (as opposed to 360 if you came at the jump straight on). In fact, you can even get away with just spinning a b/s 180, and buttering out the last 90 when you approach it from the side like this.
As you get more comfortable with the 270 spin, gradually decrease the angle you approach the jump at. Eventually you will be approaching the jump head on, and spinning a full 360. Easy as pie, it just takes a little time. Use the same concept for learning f/s 360's, and switch 360's.
you've done all this, then
start moving your way up the bigger kickers and you'll have no problem.
If all this is confusing, watch the video below. It is someone doing a f/s 360 over a hip on a skateboard. However, the principle is exactly the same. Note that he actually ONLY spins a 270 over the hip. On a trail, you are creating the "hip" by approaching the jump from the side.
Of course, the other way to do all this, is going into the terrain park. If they have a actual hips set up in the park, you can just do all of this there.
YouTube - 360 over hip