I've seen this problem a lot, the horse gets a little overambitious, and it can be really damaging for the rider, and the horse

The most effective method of fixing this I've seen is stopping the horse as soon as it starts to get silly

Once the horse starts to bomb towards the jump, either pull them back to a walk and circle away, or just circle away

Soon they'll learn that if they get stupid, they don't get to jump

Hope this helps ^^