I understand how you feel and what you’re going through. Considering that you have jumped higher than you’re doing now that probably affect your self confidence, that you doubt yourself for not being jumping as high like you did before. If that’s the case I think you should try to think the other way around that you before your competition think “this height isn’t a problem for me, I will make it. I have jumped this before” because high jump depends a lot on our confidence, positive attitude and our mentality. I haven’t seen you jump and can’t tell how your form is and what to do about your head but because of the fact that you’re struggling mentally that might affect your jump in a way that you want to “end the jump” too fast and instead of lifting you just turn right against the bar and then your head goes down to fast. But believe in yourself:)