If your elbow is hitting the floor, I would not be surprised if you were facing the wrong way. A side aerial needs to be done like a front to back cartwheel, not a side to side cartwheel. When you go into the skill you need to face the way you are going, when you come out you need to face the opposite way.
Can you post a video?
I agree very strongly that it’s not a great idea to practice these skills without supervision. A lot of kids think aerials are harmless because they think that if they don’t make it, they just out their hands down like a cartwheel. But it is not like a cartwheel. In a side aerial all the weight from a full flight skill is coming in to land on 1 leg, and that leg is at a funny angle, and if you do it incorrectly at can be at a really strange angle. It’s very easy to tear a muscle or dislocate a knee.
But it sounds like your coach is just having you throw them anyway. If she is not able to identify what you are doing wrong, even if you are in the gym you are technically doing the skill unsupervised.
Also just because you can do them on trampoline does not mean the technique is correct. The extra height the trampoline gives you can compensate for good technique and get you over with poor technique.
Ok thanks! I’ll take a video of it when I have a chance and post it!