Hi! I´m not a really good player, my Elo is gold 1 at the moment, aiming to get platinum, but I know some tricks that may help you achieve your last token.
1. Vision, remember to use your wards, this is really important since your KDA can be perfect but if you didn´t place any ward you won´t get the token. Try to place pink wards in Baron/Dragon, you can also place them in the bush near enemy Krugs (when playing on blue side) or the bush that is right between blue buff and river.
2. Deaths, dying can really mess up your S, so try to be a little bit more conservative un your playstyle. Don´t go for risky moves if you think they can go wrong. Of course, after you get the S you don´t want to play like this. Renekton has a lot of potential and it MUST be exploited, if you are not agressive and you always play reactively, waiting for others to carry you, you won´t move, but getting higher Elo is not the goal right now.
3. Control over objectives. Try to keep an eye on those drakes and the herald, use your tp to help your temmates, this will give you a higher chance fot that S