Stop being selfish: KDA is not important for grading
I was playing 
yesteraday, I was doing average in lane until bot lane fed 
and he started camping me. I was unable to do anything useful for rest of the laning phrase, basically a waveclear bot sitting mid. 
and 
were carrying the team but the useless 
and I was mis-positioning here and there getting oneshot by . At the end the enemy was literally in our base took down both nexus tower, we aced them and and I were the only two survivors.
I for some reason took 
instead of 
because I suck at laning. And I was able to to a minion wave at enemy top exposed inhib and backdoored the enemy and won the game.
At the end my KDA was 7/5/9(which isn't that high of a kda and a lot of death), only 42% kill participation, but I got a S- for this.
You can still get high grades even when you died quite a few times, so there is no need to play selfish and scared.