Okay few tips:
Use the double jump way more, when you're fighting you never wanna just stand still on the ground, It makes you an easy target for snipers. You wanna double jump around like a freakin monkey throwing those shurikens.
Also, you never wanna be on the ground except if really necesarry(such as using ulti or a guarranted kill), you need to use the enviroment way more. Like vertically.
Genji is no easy peasy hero to master, I'll tell you that, and stuff gets alot harder when you start playing with lvls 100+, but a good genji can wipe a team in seconds. So keep practicing.
(I'm no Genji master tho, since I main Tracer, but thats what I gathered from fighting them.)