Issues with horse...the sooner the better?

ok so i ride at a nice place with a nice trainer and good horses. 4 awhile jess (my trainer) has had me ride this 1 horse named armani who's a 16hh bay gelding about 13 years old. he used 2 be a super good jumper but then got lame and his owners gave him 2 where i ride. so hes good now but lately he has been BAD. i fell becuz he spooked/bucked ive fallen 1ce and almost fell 3 times in the last 2 weeks (i rode him 4 4 days). theres a horse show on the 22 and jess wants me 2 ride him. even tho im okay riding him at the barn i really dont wanna show him becuz i dont trust him and i am kinda scared. but i dont wanna tell jess that and i really dont wanna show armani. like i might be able 2 ride this other horse but idk so if i say no 2 armani and i cant ride the other horse... idk what do 2 what would u do?