Well how can i hard carry a game without tilting

Well... I know im not prefect but this mm system is pretty troll. In the last 20 games ive had a pretty good kda. but i cant carry a game with a adc 1/7 and a jg with 1/5. My main role is mid. But when i get autofilled sup i often play Leona. Whenever i do something good the adc gets all the credits. whenever i do something bad I get blamed on. In the last game i had everyone was prett y much feeding so i dont know how to hard carry every game. any tips?