I agree with Bitless; this could be a sign of fear or he could be excited.
What I would do is take it nice and slow, and if possible, suggest to your trainer to do gymnastics, or grid work. This really helps rushers! For example, set up a cross rail, then three strides away put a bigger X, then one (or whatever) put another bigger X. Or, you could use this with poles, except set a jump up in the "center" of the line.
Another tip is, are YOU relaxed? If your coming up to the jump nervous, your horse will pick up on you. Count outloud, "1-2-3-4" over & over. This will help you breath and think about your striding (another bonus!).
Half halts work wonders! Another thing I do with my horses if I feel them being rushy, I make them stop after the jump (not right after but maybe 10 strides, or so, after). It makes me feel I have them in control, and it works.
Could you possibly trot up to jumps? You as a rider could feel more comfortable with this.
And the 20M circle thing. Personally, I would not do that. Mainly, because it could teach a horse to run out.
I hope this makes sense & good luck with your horse!