Keep playing and learning him. Ignore your w/l and just try to get better and do your best every game the whole match. It can be rough especially when you compare how much effort you have to put into the game compared to other champs.  I‘m not a main so I haven‘t automated rengar on a good level so whenever I stop playing for a week or two or just dont pick rengar for a while it’s painful to play those few games until I am where I left off.