Best way to slow it all down and regain confidence?

Last thursday, was the first time i cantered my horse to a jump. we have been taking lessons since last fall. i've been riding for 40 years and the horse is an 8 yr old ottb i have owned for 3 years. long and short of it, i misunderstood my instructor, and cantered my horse to a fence before getting a feel for my just shortened stirrups. he cleared that 2 1/2 foot jump by a good extra 3 feet and catapulted me out of the tack. i was hanging in mid air, suspended far above him. through Gods Grace, when he landed it pulled me backinto the tack, but he was galloping off and i almost flipped right off the back of him with my feet flying up over his ears. i then overcompensated and fell forward, hanging from his neck and over his shoulder. he would have smashed my face into the arena wall except for when i sayed whoa, he did and i dismounted, whhile he slowd down and landed on my feet with reins in hand about 2 feet waway from the arena wall. we did finish the lesson with a cnater over a lowered fence, but my consfinence was GONE. today i tried to jog a few baby fewnces but every time we landed he really took off. and was hard to stop. what should we be doing to slow it all down again and get comfortable. the whole lesson was spent on getting him to lengthen his stride and now he seems like he is becoming A SPEED FREAK. He is a heavily raced ottb, whos brother actually won the kentucky derby. i dont want to take another 45$ an hour lesson til i have quelled the fear in me and my horse. how best to do this?