Learning is never perfect. The only way we learn is by trying to do something, observing how it went and what we want to change, then trying again. It will never be perfect or even right especially on the first try.
Being adamant that we ourselves or our horses perfectly perform, especially when learning something new, is setting you both up for frustration, anger, confusion, fear and lack of confidence. You SHOULD be making mistakes. So should your horse. That is the only way possible to learn. You need to be ok with being wrong. Like a lot. You should be comfortable making mistakes and admitting you messed up because that’s when you can start learning how to do it right.
When learning, it is also particularly important to set yourself up for success. For instance, if you’re not strong, steady and comfortable at a trot in the arena without balancing on your reins or saddle, then there is no way you should be cantering around. If you were then to be like, “Well forget the canter. Let’s go out on trail.” and your horse has a spook and tries to move out from underneath you, the likelihood of you having a wreck increases dramatically because you’re not strong and stable enough in your saddle to ride that well if you’re still struggling at the trot.
Setting good goals and milestones to help keep you safe while you are learning and making those mistakes keeps you from having a confidence crushing, traumatic event. So if your trainer says you’re not ready for something yet, thank them for keeping you safe and keep learning through your mistakes till you get to that next step and don’t rush the process.