scared

So ive been riding for 5 months now... and i decided to start jumping lessons...

yesterday i was given a new horse, ladylara... well i started off normally and when i was told to canter, the horse went crazy, she started galloping at top speed around the arena and i just couldnt get her 2 stop... she was aiming for the high jumps and i managed to steer her from jumping but then she aimed for the outside fence and i was there helplessly thinking how shes gonna throw me against the metel...she braked really hard right before she got to the fence and i fell off but grabbed onto her neck... i was terrified...

My coach explained that pulling back on the rein wont help because the horses neck is a very strong muscle,i should try to keep her in a circle to decrease her speed and avoid allowing her to run straight and pulling 1 rein back towards my knee to turn her head backwards if i wanted her 2 stop... the thing is i cantered again and i managed to keep her in a tight circle... but her canter is extremely fast and im just scared of trying any sort of jumping with her because i would imagine she would fly if i got her to jump and wouldnt stop... i guess the experience of feeling helpless on a horse is making me scared of trying jumps with her... any tips? should i insist on changing the horse? my coach says i should keep the same horse to learn how 2 control her...