As you are approaching the jump count 1,2,1,2,1,2 out load and when your saying it to yourself it should be even paced and that should help.
Set up a jump in the paddock. When going into the jump count from 6 down to 1. Always count down as it makes you look for a stride. Move the jump when you get complacent
I’m a bit new to jumping too, and have only done it for a year. However, I do a few things to help me! I always count to the beat of my horses canter. 1, 2, 3, jump. I then count the strides from a pole to the jump, usually 3, then, I keep a consistent canter all the way to the jump. I don’t let the horse speed up or slow down, and I do it until I get it right!
Another thing I do (this sounds weird but it’s very helpful!) is count my steps when I’m walking. I’ll focus on a mark on the ground, and when I feel like I’m three “strides” away, I will count 1, 2, 3, step. I hope this makes sense 😂
Lots and lots of practice. It takes time to learn to spot a distance, and once you have that you can start playing with adding and taking out strides. Work with a good trainer and do some gymnastics exercises even with poles or cavaletti to help