JemsA 360 for example is honestly easier on a big jump, you’ve got more time in the air to spot your landing and open up if you need to. Try and 360 grab a jump and progress form there.
i agree, i honestly would rather do a 3 on a big jump than a small one. it's just not a trick that lends itself to being rushed
i think you should wait til you are hitting a bigger jump that is about as big as you are comfortable on and a nice setup with a good landing, and get the speed nice and dialed. then when you're ready, keep that core flexed and your shins jammed into your boot tongues, and pop and pick up your feet and spin. you don't need to wind up really, you just need to set a nice medium pace spin.
if youre learning 3s on a tiny jump you might have been getting bad habits like winding up and throwing the spin hard, and maybe getting backseat to rush the spin around. most of that will not be the case on a bigger jump. your job on the bigger jump is to flex your core and stay on top of your skis. ya got plenty of time on a normal jump to spin 360 degrees around and spot your landing so don't rush it