How can I perfect my high jump?

So I'm an 8th grade in high jump and our coach never helps us and I've incorrectly jumped in many different ways. I would do like a straddle at the top hight with my legs open, I would do like this flip thing and land like a cannonball, and now I'm clearing up too 5ft with a combo scissor-flop. I jump... show more So I'm an 8th grade in high jump and our coach never helps us and I've incorrectly jumped in many different ways. I would do like a straddle at the top hight with my legs open, I would do like this flip thing and land like a cannonball, and now I'm clearing up too 5ft with a combo scissor-flop. I jump with a scissor then when I get in the air I get in like a sitting position at like 90 degrees with my legs and torso straight. Then I pull my legs up and I roll like a flip almost on the mat landing on my back, head, or face. (PLEASE EXCUSE ANY PUNCTUATION I'M IN A HURRY)
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